Nickel composite hydroxide and process for producing same, positive electrode active material and process for producing same, and non-aqueous electrolyte secondary battery

ABSTRACT

A positive electrode active material for a non-aqueous electrolyte secondary battery achieves high output characteristics and battery capacity, and allows a high electrode density to be achieved in the case of using the material for a positive electrode of a battery; and a non-aqueous electrolyte secondary battery uses the positive electrode active material, thereby achieving a high output with a high capacity. Prepared is a nickel composite hydroxide including plate-shaped secondary particles aggregated with overlaps between plate surfaces of multiple plate-shaped primary particles, where shapes projected from directions perpendicular to the plate surfaces of the plate-shaped primary particles are any plane projection shape of spherical, elliptical, oblong, and massive shapes, and the secondary particles have an aspect ratio of 3 to 20, and a volume average particle size (Mv) of 4 μm to 20 μm measured by a laser diffraction scattering method.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a nickel composite hydroxide and aproduction process therefor, a positive electrode active material and aproduction process therefor, and a non-aqueous electrolyte secondarybattery. More particularly, the invention relates to a nickel compositehydroxide for a precursor for a lithium-nickel composite oxide which isused as a positive electrode active material in a non-aqueouselectrolyte secondary battery such as a lithium ion secondary battery,and a production process therefor, a positive electrode active materialand a production process using a nickel composite hydroxide for aprecursor, and a non-aqueous electrolyte secondary battery that uses thepositive electrode active material. It is to be noted that the presentapplication claims priority based on the Japanese Patent Application No.2014-133402 filed on Jun. 27, 2014 in Japan.

Description of Related Art

In recent years, along with the popularization of mobile devices such ascellular phones and lap-top personal computers, the development of smalland light secondary batteries with a high energy density has beendesired strongly. Such secondary batteries include, for example, lithiumion secondary batteries that use lithium, lithium alloys, metal oxides,carbon, and the like as negative electrodes, which have been activelyresearched and developed.

Lithium ion secondary batteries that use lithium metal composite oxides,in particular, lithium-cobalt composite oxides for positive electrodeactive materials achieve high voltages on the order of 4 V, which havebeen thus expected as batteries with a high energy density, andprogressively put into practical use. Large numbers of batteries thatuse lithium-cobalt composite oxides have been ever developed in order toachieve excellent initial capacity characteristics and cyclecharacteristics, and various results have been already achieved.

Positive electrode active materials which have been ever mainly proposedcan include lithium-cobalt composite oxides (LiCoO₂) which arerelatively easily synthesized, lithium-nickel composite oxides (LiNiO₂)and lithium-nickel-cobalt-manganese composite oxides(LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂) which use more inexpensive nickel thancobalt, and lithium-manganese composite oxides (LiMn₂O₄) which usemanganese, and spherical or substantially spherical particles easilysynthesized are used mainly.

Main characteristics of batteries that use the positive electrode activematerials include a capacity and a power density, and a high powerdensity is required for, in particular, hybrid in-car batteries forwhich there has been increasing demand in recent years.

Methods for improving the power density of a battery include thereduction in the thickness of electrode films for use in secondarybatteries, and for example, in hybrid in-car batteries, films on theorder of 50 μm in thickness are used. The reason that the thickness ofelectrode films can be reduced in hybrid in-car batteries is because themovement distance of lithium ions is reduced. As just described, thereis a possibility that the positive electrode active materials for use inthin electrode films will break through the electrode films, thepositive electrode active materials are thus limited to small-sizeparticles that are uniform in particle size, and in the case ofelectrode films for hybrid in-car batteries, particles on the order of 5μm are used.

However, when such small-size particles are used for electrode films,the volume energy density which is an important characteristic alongwith the power density is disadvantageously decreased because of the lowelectrode densities.

Patent Document 1: JP 2012-84502 A

SUMMARY OF THE INVENTION

Methods for breaking through the trade-off relation include changing theshapes of commonly spherical or substantially spherical positiveelectrode active material particles, specifically into plate shapes. Theplate shapes of the positive electrode active material particles have asurface area increased as compared with spherical particles in the samevolume, and when the plate-shaped particles are oriented in electrodepreparation, a high electrode density can be achieved. Furthermore,these oriented particles which are high in aspect ratio allow thethickness of the electrode to be further reduced, and allow the outputto be further improved.

For example, Patent Literature 1 discloses, as such plate-shapedpositive electrode active material particles, plate-shaped particles forpositive electrode active materials, where primary crystal particles(particles oriented at lithium accessible surfaces) oriented such thatthe (003) plane intersects plate surfaces of the plate-shaped particles,with t≦30 and d/t≧2 when the thickness (pun), the particle size as adimension in a direction perpendicular to a thickness direction thatdefines the thickness t, and the aspect ratio are denoted respectivelyby t, d, and d/t, are dispersed in an assembly of primary crystalparticles (a large number of (003)-plane oriented particles) orientedsuch that the (003) plane is parallel to the plate surfaces of theplate-shaped particles.

However, even when the lithium accessible surfaces are oriented outsidesecondary particles as described in Patent Literature 1, outputcharacteristics will be adversely affected when the positive electrodeactive material is insufficiently brought into contact with anelectrolyte. In addition, Patent Literature 1 discloses ratecharacteristics, but fails to disclose any battery capacity itself whichis an important characteristic among battery characteristics.

As described above, it is difficult in the prior art to industriallyacquire positive electrode active materials which can form thinelectrode films with a high electrode density, and have a high capacityand excellent output characteristics.

An object of the present invention is, in view of the foregoingproblems, to provide a positive electrode active material for anon-aqueous electrolyte secondary battery which can form a thinelectrode film, achieves high output characteristics and batterycapacity, and allows a high electrode density to be achieved in the caseof using the material for a positive electrode of a battery; and anon-aqueous electrolyte secondary battery that uses the positiveelectrode active material, thereby achieving a high output with a highcapacity.

In addition, an object of the present invention is to provide a nickelcomposite hydroxide as a precursor for a positive electrode activematerial, which makes it possible to provide a positive electrode activematerial for such a non-aqueous electrolyte secondary battery.

Therefore, the inventors have earnestly carried out studies on positiveelectrode active materials for non-aqueous electrolyte secondarybatteries, which have shapes capable of achieving a high electrodedensity, and nickel composite hydroxides as precursors for the positiveelectrode active materials. As a result, the inventors have found thatthe control of the compositions of the nickel composite hydroxidesduring crystallization and the crystallization conditions achievesplate-shaped secondary particles aggregated with overlaps between platesurfaces of multiple plate-shaped primary particles.

Furthermore, the inventors have found that the foregoing nickelcomposite hydroxide is mixed with a lithium compound, and subjected tocalcination, thereby providing a positive electrode active materialwhich takes over the shape of the nickel composite hydroxide, therebymaking it possible to achieve a balance between high outputcharacteristics and battery capacity and a high electrode density, andthus achieved the present invention.

More specifically, a nickel composite hydroxide according to the presentinvention for achieving the object is a nickel composite hydroxiderepresented by N_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (x, y, z, and A inthe formula fall within ranges of: 0<x≦0.35; 0≦y≦0.35; 0≦z≦0.1; and0≦A≦0.5, x, y, and z meet 0<x+y+z≦0.7, and M in the formula representsat least one additive element selected from V, Mg, Al, Ti, Mo, Nb, Zr,and W), the nickel composite hydroxide characteristically includingplate-shaped secondary particles aggregated with overlaps between platesurfaces of multiple plate-shaped primary particles, where shapesprojected from directions perpendicular to the plate surfaces of theplate-shaped primary particles are any plane projection shape ofspherical, elliptical, oblong, and massive shapes, and the secondaryparticles have an aspect ratio of 3 to 20, and a volume average particlesize (Mv) of 4 μm to 20 μm measured by a laser diffraction scatteringmethod.

The nickel composite hydroxide is preferably 0.70 or less in[(D90−D10)/Mv] indicating a particle size variation index, which iscalculated from D90 and D10 in a particle size distribution obtained bya laser diffraction scattering method and the volume average particlesize (Mv).

In addition, in the nickel composite hydroxide, the average value ispreferably 1 μm to 5 μm for the maximum diameters of the plate-shapedprimary particles projected from directions perpendicular to platesurfaces of the secondary particles.

Furthermore, the nickel composite hydroxide preferably has at least aconcentration layer of cobalt, and the concentration layer is preferably0.01 μm to 1 μm in thickness.

A process for producing a nickel composite hydroxide according to thepresent invention is a production process for producing a nickelcomposite hydroxide represented byNi_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (x, y, z, and A in the formulafall within ranges of: 0<x≦0.35; 0≦y≦0.35; 0≦z≦0.1; and 0≦A≦0.5, x, y,and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W), theprocess characteristically including: a nucleation step of generatingplate-shaped crystal nuclei by adjusting an aqueous solution fornucleation, including a metal compound containing cobalt, where thecontent of cobalt is 90 atom % or more with respect to all metalelements, to an pH value of 12.5 or more on the basis of a liquidtemperature of 25° C. in a non-oxidizing atmosphere with an oxygenconcentration of 5 volume % or less; and a particle growth step ofcausing growth of the plate-shaped crystal nuclei until the aspect ratiofalls within the range of 3 to 20, by adjusting slurry for particlegrowth, containing the plate-shaped crystal nuclei formed in thenucleation step, in a non-oxidizing atmosphere with an oxygenconcentration of 5 volume % or less, such that the pH value of theslurry is 10.5 to 12.5 on the basis of a liquid temperature of 25° C.,and lower than the pH value in the nucleation step, and supplying amixed aqueous solution including a metal compound containing at leastnickel to the slurry for particle growth.

In the process for producing a nickel composite hydroxide, nucleation ispreferably developed in a non-oxidizing atmosphere with an oxygenconcentration of 2 volume % or less in the nucleation step, and theammonia concentration of the slurry for particle growth is preferablyadjusted to 5 g/L to 20 g/L in the particle growth step.

In addition, in the process for producing a nickel composite hydroxide,plate-shaped crystal nucleus-containing slurry with a pH value adjustedis used as the slurry for particle growth, the plate-shaped crystalnucleus-containing slurry containing the plate-shaped crystal nucleiobtained in the nucleation step.

A positive electrode active material for a non-aqueous electrolytesecondary battery according to the present invention is a positiveelectrode active material for a non-aqueous electrolyte secondarybattery, the positive electrode active material including alithium-nickel composite oxide represented byLi_(1+u)Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)O₂ (u, x, y, and z in the formulafall within ranges of: −0.05≦u≦0.50; 0<x≦0.35; 0≦y≦0.35; and 0≦z≦0.1, x,y, and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W), thelithium-nickel composite oxide having a hexagonal layered structure,characteristically where lithium-nickel composite oxide includesplate-shaped secondary particles aggregated with overlaps between platesurfaces of multiple plate-shaped primary particles, shapes projectedfrom directions perpendicular to the plate surfaces of the plate-shapedprimary particles are any plane projection shape of spherical,elliptical, oblong, and massive shapes, and the secondary particles havean aspect ratio of 3 to 20, and a volume average particle size (Mv) of 4μm to 20 μm measured by a laser diffraction scattering method.

In the positive electrode active material for a non-aqueous electrolytesecondary battery, the specific surface area is preferably 0.3 m²/g to 2m²/g, and the [(D90−D10)/Mv] indicating a particle size variation indexis preferably 0.75 or less, which is calculated from D90 and D10 in aparticle size distribution obtained by a laser diffraction scatteringmethod and the volume average particle size (Mv).

In addition, in the positive electrode active material for a non-aqueouselectrolyte secondary battery, the site occupancy is preferably 7% orless at 3 a sites with metal ions other than lithium, and the siteoccupancy is preferably 7% or less at 3 b sites with lithium ions, thesite occupancies obtained from Rietveld analysis with X-ray diffractionanalysis, and the orientation index at a (003) plane is preferably 0.9to 1.1, which is found by X-ray diffraction analysis.

A process for producing a positive electrode active material for anon-aqueous electrolyte secondary battery according to the presentinvention is a process for producing a positive electrode activematerial for a non-aqueous electrolyte secondary battery, the positiveelectrode active material including a lithium-nickel composite oxiderepresented by Li_(1+u)Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)O₂ (u, x, y, and zin the formula fall within ranges of: −0.05≦u≦0.50; 0<x≦0.35; 0≦y≦0.35;and 0≦z≦0.1, x, y, and z meet 0<x+y+z≦0.7, and M in the formularepresents at least one additive element selected from V, Mg, Al, Ti,Mo, Nb, Zr, and W), the lithium-nickel composite oxide having ahexagonal layered structure, the process characteristically including: amixing step of forming a lithium mixture by mixing the nickel compositehydroxide with a lithium compound; and a calcining step of calcining thelithium mixture formed in the mixing step at a temperature of 650° C. to980° C. in an oxidizing atmosphere.

In the process for producing a positive electrode active material for anon-aqueous electrolyte secondary battery, the ratio (Li/Me) of thelithium atom number (Li) to the sum (Me) of the atom numbers of metalsother than lithium included in the lithium mixture is preferably 0.95 to1.5.

In addition, the process for producing a positive electrode activematerial for a non-aqueous electrolyte secondary battery preferablyfurther includes, before the mixing step, a heat treatment step ofapplying a heat treatment to the nickel composite hydroxide at atemperature of 300° C. to 750° C. in a non-reducing atmosphere.

Furthermore, in the process for producing a positive electrode activematerial for a non-aqueous electrolyte secondary battery, the oxidizingatmosphere in the calcining step is preferably an atmosphere containing18 volume % to 100 volume % of oxygen.

A non-aqueous electrolyte secondary battery according to the presentinvention has a positive electrode, a negative electrode, a non-aqueouselectrolyte, and a separator, and the positive electrode ischaracteristically formed from the above-mentioned positive electrodeactive material for a non-aqueous electrolyte secondary battery.

According to the present invention, the nickel composite hydroxide canbe obtained which is preferred as a precursor for a positive electrodeactive material for a non-aqueous electrolyte secondary battery.

According to the present invention, when the nickel composite hydroxideis used as a precursor for a positive electrode active material of anon-aqueous electrolyte secondary battery, a positive electrode activematerial can be obtained which provides high output characteristics andbattery capacity, and allows a high electrode density to be achieved.

According to the present invention, when the positive electrode activematerial is applied to a non-aqueous electrolyte secondary battery, athin electrode film can be formed, and a non-aqueous electrolytesecondary battery can be achieved which has high output characteristicsand battery capacity while achieving a balance therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a process for producing a nickel compositehydroxide in accordance with the present invention applied.

FIG. 2 is a flowchart showing a process for producing a nickel compositehydroxide in accordance with the present invention applied, whichdiffers in nucleation step from the production process shown in FIG. 1.

FIG. 3 is a flowchart showing a process for producing a nickel compositehydroxide in accordance with the present invention applied, whichdiffers in particle growth step from the production process shown inFIG. 1.

FIG. 4 is a schematic cross-sectional view of a coin-type battery foruse in battery evaluation.

FIG. 5 is a scanning electron micrograph (1000-fold magnification forobservation) of a nickel composite hydroxide obtained according toExample 1.

FIG. 6 is a scanning electron micrograph (1000-fold magnification forobservation) of a nickel composite hydroxide obtained according toComparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments (hereinafter, referred to as “the presentembodiments”) in accordance with the present invention applied will bedescribed in detail with reference to the drawings with respect to thefollowing items. It is to be noted that the present invention is not tobe considered limited to the following embodiments, but variousmodifications can be made without departing from the scope of thepresent invention.

[1] Nickel Composite Hydroxide and Production Process therefor

[2] Positive Electrode Active Material for Non-Aqueous ElectrolyteSecondary Battery and Production Process therefor

[3] Non-aqueous Electrolyte Secondary Battery

[1] Nickel Composite Hydroxide and Production Process Therefor

<1-1> Nickel Composite Hydroxide

The nickel composite hydroxide according to the present embodimentincludes plate-shaped secondary particles aggregated with overlapsbetween plate surfaces of multiple plate-shaped primary particles, whereshapes projected from directions perpendicular to the plate surfaces ofthe plate-shaped primary particles are any plane projection shape ofspherical, elliptical, oblong, and massive shapes, and the secondaryparticles have an aspect ratio of 3 to 20, and a volume average particlesize (Mv) of 4 μm to 20 μm measured by a laser diffraction scatteringmethod.

The inventors have found, as a result of studying the filling density ofa positive electrode active material in a positive electrode and thearea of contact with an electrolytic solution, that the use of apositive electrode active material composed of plate-shaped secondaryparticles aggregated with overlaps between plate surfaces ofplate-shaped primary particles makes it possible to achieve a balancebetween an improved filling density and an increased area of contactwith an electrolytic solution. More specifically, the inventors havefound that the use of plate-shaped secondary particles aggregated withoverlaps between the plate surfaces of the plate-shaped primaryparticles where shapes projected from directions perpendicular to theplate surfaces are any plane projection shape of circular, elliptical,oblong, and massive shapes achieves, at the same time, the effects of:ingress of a sufficient amount of electrolytic solution into thesecondary particles; an increased area of contact with the electrolyticsolution; and further, an improved density of filling with theplate-shaped particles.

(Particle Shape and Structure)

The nickel composite hydroxide is composed of plate-shaped secondaryparticles aggregated with overlaps between plate surfaces of multipleplate-shaped primary particles, and furthermore, the shapes projectedfrom directions perpendicular to plate surfaces of the plate-shapedprimary particles are any plane projection shape of circular,elliptical, oblong, and massive shapes. In this regard, the platesurface means a surface perpendicular to a projection directioncorresponding to the maximum projected area of the particle. Inaddition, the overlaps between the plate surfaces may be tilted fromdirections corresponding to the plate surfaces parallel to each other,to such an extent that the plate-shaped primary particles are easilyaggregated with each other.

The shape of a positive electrode active material particle is supposedto take over the shape of a nickel composite hydroxide particle as aprecursor of the positive electrode active material particle(hereinafter, also referred to as a “precursor particle”). Therefore,controlling the shapes of the precursor particles in accordance withplate-shaped secondary particles aggregated with overlaps between platesurfaces of plate-shaped primary particles can also turn the shapes ofobtained positive electrode active material particles into similarlycharacteristic shapes. It is to be noted that in the case of usingsmall-size or plate-shaped precursor particles as used conventionally,positive electrode active material particles are obtained which takeover the shapes of the conventional precursor particles, thereby failingto obtain positive electrode active materials as will be describedlater.

In addition, the secondary particles have an aspect ratio of 3 to 20,preferably 5 to 20, and the nickel composite hydroxide has a volumeaverage particle size (Mv) of 4 μm to 20 μm measured by a laserdiffraction scattering method. Furthermore, in the nickel compositehydroxide, the average value (R1) is preferably 1 μm to 5 μm for themaximum diameters of shapes projected from directions perpendicular toplate surfaces of plate-shaped primary particles (the maximum diametersof plate-shaped primary particles projected from directionsperpendicular to plate surfaces of secondary particles). When the aspectratio and Mv that identify the shape of the nickel composite hydroxide(hereinafter, also referred to as “shape-specifying values”) go beyondthe respective ranges, the shape-specifying values of a positiveelectrode active material obtained can also depart from respectiveranges, thus failing to achieve the effect of achieving high outputcharacteristics and battery capacity, thereby making it possible toachieve a high electrode density as will be described later.Accordingly, there is need for the shape-specifying values (aspectratio, Mv) to fall within the respective ranges in the nickel compositehydroxide. In addition, R1 is preferably adapted to fall within therange mentioned above, in order to achieve higher output characteristicsand battery capacity.

In this regard, the aspect ratio means the ratio (R2/t) of the averagevalue (R2) for the maximum diameters of the secondary batteries,projected from directions perpendicular to the plate surfaces of thesecondary particles, to the average value (t) for the maximumthicknesses in directions perpendicular to the plate surfaces. Theaverage value (t) for the maximum thicknesses is obtained by measuringand averaging any twenty or more secondary particles observable fromdirections parallel to the plate surfaces in appearance observation witha scanning electron microscope. In addition, the average value (R2) forthe maximum diameters is obtained by measuring and averaging fromobservation of any twenty or more secondary particles observable fromdirections perpendicular to the plate surfaces in appearance observationwith a scanning electron microscope. The R2/t is obtained from therespectively obtained maximum thickness (t) and average value (R2) forthe maximum diameters, and regarded as the aspect ratio for thesecondary particles. In addition, the average value (R1) for the maximumdiameters of the plate-shaped primary particles is obtained by measuringand averaging, in the same way as R2, any fifty or more primaryparticles observable entirely from directions perpendicular to the platesurfaces.

The nickel composite hydroxide is composed of plate-shaped secondaryparticles aggregated with overlaps between plate surfaces of multipleplate-shaped primary particles, and the secondary particles thus havesufficient voids produced therein. In particular, the shapes projectedfrom directions perpendicular to the plate surfaces of the plate-shapedprimary particles are any plane projection shape of circular,elliptical, oblong, and massive shapes, and surfaces parallel to theplate surfaces are thus also configured to have sufficient voidstherein. Thus, in the preparation of a positive electrode activematerial, when the nickel composite hydroxide and a lithium compound aremixed and calcined, the melted lithium compound is distributed into thesecondary particles, and lithium is diffused sufficiently, therebymaking it possible to obtain a positive electrode active material withfavorable crystallinity. On the other hand, plate-shaped secondaryparticles formed as polycrystalline bodies from primary particles arenot configured to have sufficient voids between the primary particles,and the melted lithium compound is distributed insufficiently into thesecondary particles. The voids in the secondary particles in the nickelcomposite hydroxide are left even after a positive electrode activematerial is obtained, thus making it possible to distribute anelectrolyte into the secondary particles in the positive electrodeactive material.

Furthermore, in the case in accordance with a process for producing anickel composite hydroxide as will be described later, the nickelcomposite hydroxide has a concentration layer of cobalt within theprimary particles. The secondary particles are formed by causing growthof plate-shaped crystal nuclei produced from a metal compound containingcobalt. Accordingly, a high-concentration layer of cobalt based on theplate-shaped crystal nuclei comes to be present within the primaryparticles of the nickel composite hydroxide formed. When theplate-shaped crystal nuclei are developed to such an extent that thehigh concentration layer is formed, the primary particles are developedinto desired shapes, and furthermore, the plate-shaped secondaryparticles are formed by aggregation with overlaps between the platesurfaces of the primary particles. On the other hand, in the absence ofa high-concentration layer, the plate-shaped crystal nuclei can beconsidered non-fully developed, and secondary particles obtained mayfail to have a desired shape. However, plate-shaped particles that havesuch strength to an extent that the particles are not broken duringparticle growth, and have shapes equivalent to the plate-shaped crystalnuclei mentioned above can be used as plate-shaped crystal nuclei todevelop primary particles, and then form secondary particles, and thus,when plate-shaped particles of desired compositions in desired shapesare prepared separately to obtain nickel composite hydroxides, some ofthe hydroxides are obtained without the high concentration layermentioned above.

In order to develop the primary particles, and make the shapes of thesecondary particles adequate, the high-concentration layer is preferably0.01 μm to 1 μm in thickness. The thickness of less than 0.01 μm maybreak down the plate-shaped crystal nuclei during nucleation or duringparticle growth, thereby resulting in inadequate development of primaryparticles. On the other hand, the thickness in excess of 1 μm may makethe composition of an obtained positive electrode active materialheterogeneous in particles, or fail to develop primary particles intoplate shapes.

The crystal growth from the plate-shaped crystal nuclei is developed atboth sides of the plate-shaped crystal nuclei, thereby making ispossible to develop primary particles into plate shapes with high aspectratios, and the primary particles preferably have the nuclei in centralparts in the thickness direction.

(Composition)

The nickel composite hydroxide has a composition represented by thegeneral formula (1): Ni_(1-y-x-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (in theformula, x, y, z, and A fall within the ranges of: 0<x≦0.35; 0≦y≦0.35;0≦z≦0.1; and 0≦A≦0.5, x, y, and z meet 0<x+y+z≦0.7, and M in the formularepresents at least one additive element selected from V, Mg, Al, Ti,Mo, Nb, Zr, and W).

The nickel composite hydroxide contains at least cobalt as describedabove. x in the general formula (1), which represents the cobaltcontent, meets 0<x≦0.35, and preferably meets 0.05<x≦0.35, morepreferably 0.1≦x≦0.35 in order to develop the plate-shaped crystalnuclei sufficiently.

When a positive electrode active material is obtained with theabove-mentioned nickel composite hydroxide as a raw material, thecomposition ratio (Ni:Co:Mn:M) of the composite hydroxide is maintainedin the positive electrode active material obtained. Therefore, thecomposition ratio of nickel composite hydroxide particles is adapted tobe equal to the composition ratio required for a positive electrodeactive material to be obtained. The composition indicated in the generalformula (1) allows, when the obtained positive electrode active materialfor a non-aqueous electrolyte secondary battery is used for a battery,the battery to provide superior performance.

(Particle Size Distribution)

The nickel composite hydroxide is preferably 0.70 or less in[(D90−D10)/Mv] indicating a particle size variation index, which iscalculated from D90 and D10 in a particle size distribution obtained bya laser diffraction scattering method and the volume average particlesize (Mv).

The particle size distribution of the positive electrode active materialis strongly affected by the nickel composite hydroxide as a precursor,and thus, when the nickel composite hydroxide has fine particles orcoarse particles mixed therein, similar particles will also come to bepresent in the positive electrode active material. More specifically,when the nickel composite hydroxide has a variation index in excess of0.70 in a wide particle size distribution, the positive electrode activematerial may also have fine particles or coarse particles.

Accordingly, the adjustment of the variation index of the nickelcomposite hydroxide to 0.70 or less can reduce the variation index ofthe positive electrode active material obtained, and thus improve cyclecharacteristics and output characteristics. While the reduced variationindex can improve properties of the positive electrode active material,it is difficult to keep the particle size completely from varying, andthe variation index has a realistic lower limit on the order of 0.30.

In the [(D90−D10)/Mv] indicating the particle size variation index, D10means a particle size at which the accumulated volume accounts for 10%of the total volume of all particles when the number of particles ateach particle size is accumulated in order of increasing the particlesize. In addition, D90 means a particle size at which the accumulatedvolume accounts for 90% of the total volume of all particles when thenumber of particles is accumulated in the same way. The volume averageparticle size Mv and D90 and D10 can be measured with the use of a laserdiffraction-scattering type particle size analyzer.

The nickel composite hydroxide as described above characteristicallyincludes plate-shaped secondary particles aggregated with overlapsbetween plate surfaces of multiple plate-shaped primary particles, wherethe shapes projected from directions perpendicular to the plate surfacesof the plate-shaped primary particles are any plane projection shape ofspherical, elliptical, oblong, and massive shapes, and the secondaryparticles have an aspect ratio of 3 to 20, and a volume average particlesize (Mv) of 4 μm to 20 μm measured by a laser diffraction scatteringmethod.

This nickel composite hydroxide is preferred as a precursor for apositive electrode active material of a non-aqueous electrolytesecondary battery. More specifically, the use of the nickel compositehydroxide as a precursor for a positive electrode active material canincrease, because the hydroxide has features as described above, thearea of contact with an electrolytic solution, thereby achieving apositive electrode active material with a high filling density. As aresult, this nickel composite hydroxide can form a thin electrode film,thereby achieving high output characteristics and battery capacity, andthus achieving a positive electrode active material for a non-aqueouselectrolyte secondary battery which has a high electrode density.

<1-2> Process for Producing Nickel Composite Hydroxide

The process for producing the nickel composite hydroxide is intended toproduce, through a crystallization reaction, a nickel compositehydroxide represented by the general formula (1):Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (x, y, z, and A in the formulafall within ranges of: 0<x≦0.35; 0≦y≦0.35; 0≦z≦0.1; and 0≦A≦0.5, x, y,and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W).

<1-2-1> Nucleation Step and Particle Growth Step

The process for producing the nickel composite hydroxide includes: asshown in FIG. 1, a nucleation step of generating plate-shaped crystalnuclei from an aqueous solution for nucleation, which includes a metalcompound containing cobalt, where the content of cobalt is 90 atom % ormore with respect to all metal elements; and a particle growth step ofcausing growth of the plate-shaped crystal nuclei formed in thenucleation step.

In this regard, conventional crystallization methods cause a nucleationreaction and a particle growth reaction to proceed simultaneously in thesame tank. For this reason, it has been difficult for the conventionalcrystallization methods to control particle shapes, due to isotropicgrowth of composite hydroxide particles obtained.

In contrast, the process for producing the nickel composite hydroxideaccording to the present embodiment carries out, in a clearly separatedmanner, the nucleation step of generating plate-shaped crystal nucleimainly by a nucleation reaction, and the particle growth step of causinggrowth of particles mainly on both sides of the plate-shaped crystalnuclei. Thus, the process for producing the nickel composite hydroxidecan control the particle shape of the nickel composite hydroxideobtained. Methods for the separation can include a method of changingthe pH value for the nucleation step and the pH value for the particlegrowth step, and a method of changing the reaction tank for thenucleation step and the reaction tank for the particle growth step, aswill be described later.

(Nucleation Step)

In the nucleation step, an aqueous solution for nucleation, which isobtained by dissolving a metal compound containing cobalt in water in apredetermined proportion, is controlled such that the pH value on thebasis of a liquid temperature of 25° C. is 12.5 or more, therebygenerating plate-shaped crystal nuclei.

The crystal nuclei correspond to the concentration layer of cobalt asdescribed above, that is, a layer containing a high concentration ofcobalt, which can also contain metal elements other than cobalt. Inorder to develop plate-shaped fine crystal nuclei, the content of cobaltincluded in the crystal nuclei is adjusted to 90 atomic % or more, morepreferably 95 atomic % or more with respect to all of the metalelements. In order to fully develop fine plate-shaped crystal nuclei,the crystal nuclei preferably include only a hydroxide of cobalt.

In the nucleation step, first, an aqueous solution for nucleation isprepared by dissolving, in water, a metal compound containing cobalt andother metal compounds so as to reach the composition of the crystalnuclei.

Next, an inorganic alkaline aqueous solution is added to the preparedaqueous solution for nucleation, thereby controlling the pH value of theaqueous solution for nucleation so as to be 12.5 or more on the basis ofa liquid temperature of 25° C., and lower than the pH in the nucleationstep. The pH value of the aqueous solution for nucleation is measurablewith a common pH meter.

In the nucleation step, with the desired composition of the aqueoussolution for nucleation, the pH value is adjusted to 12.5 or more at aliquid temperature of 25° C., thereby developing a plate-shaped nucleus,and generating a fine plate-shaped crystal nucleus on a preferentialbasis. Thus, in the nucleation step, fine plate-shaped crystal nucleifor a composite oxide containing cobalt are generated in the aqueoussolution for nucleation, thereby providing plate-shaped crystalnuclei-containing slurry (also referred to as “plate-shaped crystalnucleus slurry”).

The nucleation step is not limited to the process shown in FIG. 1, butmay be carried out in accordance with, for example, a process as shownin FIG. 2. In the nucleation step shown in FIG. 1, the inorganicalkaline aqueous solution is added directly to the aqueous solution fornucleation, thereby generating the plate-shaped crystal nuclei.

On the other hand, in the nucleation step shown in FIG. 2, whilestirring, in a reaction tank, a reaction aqueous solution with a pHvalue adjusted to 12.5 or more by adding water to an inorganic alkalineaqueous solution in advance, an aqueous solution for nucleation issupplied thereto, thereby generating plate-shaped crystal nuclei whilemaintaining the pH value with the addition of the inorganic alkalineaqueous solution, and thus providing plate-shaped crystal nucleusslurry. The process of supplying the aqueous solution for nucleationwhile maintaining the pH value of the reaction aqueous solution ispreferred, because the process can strictly control the pH value,thereby easily generating plate-shaped crystal nuclei.

When predetermined amounts of crystal nuclei are generated in theplate-shaped crystal nucleus slurry from the aqueous solution fornucleation and the inorganic alkaline aqueous solution in the nucleationsteps shown in FIGS. 1 and 2, the nucleation steps are completed.Whether predetermined amounts of crystal nuclei are generated or not isdetermined by the amounts of metal salts added to the aqueous solutionfor nucleation.

The amounts of nuclei generated in the nucleation steps are not to beconsidered particularly limited, but preferably 0.1% to 2%, preferably0.1% to 1.5% of the total amount, that is, the total metal salt suppliedfor obtaining the nickel composite hydroxide particles, in order toobtain nickel composite hydroxide particles where the shape-specifyingvalues described above fall within the respective ranges.

(Particle Growth Step)

Next, the process proceeds to the particle growth step. In the particlegrowth step, after the completion of the nucleation step, the pH valueof the plate-shaped crystal nucleus slurry in the reaction tank isadjusted so as to be 10.5 to 12.5, preferably 11.0 to 12.0 on the basisof a liquid temperature of 25° C., and lower than the pH in thenucleation step, thereby providing slurry for particle growth in theparticle growth step. Specifically, the pH value is controlled byadjusting the amount of the inorganic alkaline aqueous solutionsupplied. It is to be noted that the particle growth steps shown inFIGS. 1 and 2 are carried out in the same way.

In the particle growth step, a mixed aqueous solution including a metalcompound containing at least nickel is supplied to the slurry forparticle growth. The mixed aqueous solution contains, in addition to themetal compound containing nickel, a metal compound containing cobalt,manganese, or an additive element, if necessary, so as to achieve anickel composite hydroxide with a predetermined composition ratio. Inthe particle growth step, the composition ratio of metals in primaryparticles that grow with the plate-shaped crystal nuclei as nuclei isequal to the composition ratio of respective metals in the mixed aqueoussolution. On the other hand, in the nucleation step, the compositionratio of metal in the plate-shaped crystal nuclei is equal to thecomposition ratio of respective metals in the aqueous solution fornucleation. Therefore, an adjustment is made such that the total of themetal salt for use in the nucleation step and the metal salt in themixed aqueous solution for use in the particle growth step provides thecomposition ratio of respective metals in the nickel compositehydroxide.

In the particle growth step, the pH value of the slurry for particlegrowth is made in the range of 10.5 to 12.5, preferably 11.0 to 12.0 onthe basis of a liquid temperature of 25° C., and made lower than the pHof the nucleation step, thereby coming to cause the growth reaction ofcrystal nuclei preferentially rather than the generation reaction forcrystal nuclei. Thus, in the particle growth step, the plate-shapedcrystal nuclei come to undergo particle growth, almost without newnucleation in the slurry for particle growth.

In the particle growth step, in order to cause the produced nickelcomposite hydroxide to have the composition shown in the general formula(1) described above, the content of cobalt in the mixed aqueous solutionis made lower than that in the aqueous solution for nucleation, withoutgenerating fine plate-shaped crystal nuclei. Thus, the plate-shapedcrystal nuclei undergo particle growth to form plate-shaped primaryparticles that have, in central parts thereof, a high-concentrationlayer containing cobalt, and the primary particles aggregate so as tooverlap each other, thereby providing nickel composite hydroxideparticles.

Because the pH value of the slurry for particle growth varies with theparticle growth through the supply of the mixed aqueous solution, theinorganic alkaline aqueous solution is also supplied to the slurry forparticle growth, besides to the mixed aqueous solution, therebycontrolling the pH value of the slurry for particle growth so as to keepthe range of 10.5 to 12.5 on the basis of a liquid temperature of 25° C.

Thereafter, when the nickel composite hydroxide particles grow to apredetermined particle size and aspect ratio, the particle growth stepis completed. The particle size and aspect ratio for the nickelcomposite hydroxide particles can be determined easily from the additiveamounts of the metal salts in the respective steps, when a preliminarytest is carried out to obtain the relationship between the additiveamounts of metal salts respectively for use in the respective steps ofthe nucleation step and particle growth step and particles obtained.

As described above, in the process for producing the nickel compositehydroxide, plate-shaped crystal nuclei are generated preferentially inthe nucleation step, and thereafter, in the particle growth step, thegrowth to plate-shaped primary particles and the generation of secondaryparticles by the aggregation of the plate-shaped primary particles arecaused only, almost without generating new crystal nucleation. Thus,homogeneous plate-shaped crystal nuclei can be formed in the nucleationstep, and the plate-shaped crystal nuclei are allowed to undergoparticle growth homogeneously in the particle growth step. In addition,the growth to plate-shaped primary particles proceeds homogeneouslywithout nucleation, and the aggregation of the plate-shaped primaryparticles thus also proceeds homogeneously. Accordingly, in theabove-described process for producing the nickel composite hydroxide,homogeneous nickel composite hydroxide particles can be obtained whichare controlled into a desired shape with a narrow range of particle sizedistribution.

It is to be noted that in the process for producing the nickel compositehydroxide, metal ions are crystallized as plate-shaped crystal nuclei orcomposite hydroxide particles in the both steps, thus increasing theproportion of the liquid component to the metal component in eachslurry. In this case, apparently, the concentrations of the metal saltssupplied are decreased, and in particular, in the particle growth step,there is a possibility that composite hydroxide particles will growinsufficiently.

Therefore, in order to keep the liquid component from being increased,the work of partially eliminating, from the reaction tank, the liquidcomponent in the slurry for particle growth is preferably conductedbetween after the completion of the nucleation step and in the processof particle growth step. Specifically, for example, the supply of theinorganic alkaline aqueous solution and mixed aqueous solution to theslurry for particle growth, and stirring are stopped once, therebycausing the plate-shaped crystal nuclei and the nickel compositehydroxide particles to settle out, and supernatant is eliminated fromthe slurry for particle growth. This work can increase the relativeconcentration of the mixed aqueous solution in the slurry for particlegrowth. Further, with the increased relative concentration of the mixedaqueous solution, nickel composite hydroxide particles are allowed togrow, thus making it possible to make the particle size distribution ofthe nickel composite hydroxide particles narrower, and also increase thedensity of the nickel composite hydroxide particles as whole secondaryparticles.

In addition, in the particle growth steps shown in FIGS. 1 and 2, the pHvalue of the plate-shaped crystal nucleus slurry obtained in nucleationstep is adjusted to obtain slurry for particle growth, thereby carryingout the particle growth steps continuously from the nucleation steps,and the processes thus have the advantage of being able to proceed tothe particle growth steps rapidly. Furthermore, the processes canproceed from the nucleation steps to the particle growth steps justthrough the adjustment of the pH value of the plate-shaped crystalnucleus slurry, and have the advantage of being also able to adjust thepH value easily by only temporarily stopping the supply to the inorganicalkaline aqueous solution, or adding a sulfuric acid to the plate-shapedcrystal nucleus slurry in the case of the same type of inorganic acid asthe acid constituting the metal compound, for example, a sulfate.

In this regard, the particle growth step is not limited to the processesshown in FIGS. 1 and 2, but may be the process shown in FIG. 3. Thenucleation step shown in FIG. 3 can be achieved by adding an inorganicalkaline aqueous solution directly to an aqueous solution for nucleationin the same way as the nucleation step shown in FIG. 1, or stirring areaction aqueous solution and supplying an aqueous solution fornucleation while adjusting the pH value in the same way as thenucleation step shown in FIG. 2.

In the particle growth step shown in FIG. 3, separately fromplate-shaped crystal nucleus slurry, an aqueous solution for pH valueadjustment is prepared which is adjusted with the inorganic alkalineaqueous solution to a pH value suitable for the particle growth step.Then, plate-shaped crystal nucleus slurry produced by carrying out thenucleation step in a separate reaction tank, preferably the plate-shapedcrystal nucleus slurry with a liquid component partially removedtherefrom as described above, is added to the aqueous solution for pHvalue adjustment, thereby providing slurry for particle growth. Theparticle growth step is carried out in the same way as the particlegrowth steps shown in FIGS. 1 and 2 with the use of the slurry forparticle growth.

The process for producing the nickel composite hydroxide as shown inFIG. 3 can separate the nucleation step and the particle growth step ina more reliable manner, and thus turn the condition of the reactionaqueous solution in each step into an optimal condition for each step.In particular, from the start point of the particle growth step, the pHvalue of the slurry for particle growth can be turned into an optimalcondition. The nickel composite hydroxide obtained in the particlegrowth step can be adapted to have a narrower range of particle sizedistribution, and made homogeneous.

<1-2-2> Control of pH and Reaction Atmosphere, Particle Size, AmmoniaConcentration

Next, the control of the pH and reaction atmosphere, the particle sizeof the nickel composite hydroxide, and the ammonia concentration in eachstep will be described in detail.

(pH Control in Nucleation Step)

As described above, in the nucleation steps in FIGS. 1 to 3, there is aneed to control the pH value of the aqueous solution for nucleation soas to fall within the range of 12.5 or more on the basis of a liquidtemperature of 25° C. When the pH value on the basis of a liquidtemperature of 25° C. is less than 12.5, plate-shaped crystal nucleithemselves increase while the crystal nuclei are generated, thus failingto obtain plate-shaped secondary particles with plate-shaped primaryparticles aggregated in the subsequent particle growth step. On theother hand, finer plate-shaped crystal nuclei are obtained as the pHvalue is larger, but when the pH value exceeds 14.0, problems may becaused, such as the reaction solution gelled, thereby makingcrystallization difficult, and excessively small plate-shaped primaryparticles of the nickel composite hydroxide. More specifically, in thenucleation step, the pH value of the aqueous solution for nucleation isadapted to fall within the range of 12.5 or more, preferably 12.5 to14.0, more preferably 12.5 to 13.5, thereby making it possible togenerate plate-shaped crystal nuclei sufficiently.

(pH Control in Particle Growth Step)

In the particle growth step, there is a need to control the pH value ofthe slurry for particle growth so as to fall within the range of 10.5 to12.5, preferably 11.0 to 12.0 on the basis of a liquid temperature 25°C., and to be lower than the pH in the nucleation step. When the pHvalue on the basis of a liquid temperature of 25° C. is less than 10.5,there are more impurities included in the nickel composite hydroxideobtained, for example, more anion constituent elements included in themetal salts. Alternatively, when the value exceeds pH 12.5, new crystalnuclei will be generated in the particle growth step, thereby worseningthe particle size distribution. More specifically, in the particlegrowth step, the pH value of the slurry for particle growth iscontrolled to fall within the range of 10.5 to 12.5 and to be lower thanthe pH in the nucleation step, thereby making it possible to cause onlygrowth of the plate-shaped crystal nuclei generated in the nucleationstep to plate-shaped primary particles and aggregation of theplate-shaped primary particles on a preferential basis, and inhibit newcrystal nucleation, and the nickel composite hydroxide obtained can beadapted to be homogeneous, narrow in particle size distribution range,and controlled in shape. In order to separate the nucleation and theparticle growth in a clearer manner, the pH value of the slurry forparticle growth is preferably controlled to be lower than the pH in thenucleation step by 0.5 or more, more preferably 1.0 or more.

In each of the nucleation step and particle growth step, the range ofvariation in pH preferably falls within ±0.2 from the set value. Whenthe range of variation in pH is large, the nucleation and the particlegrowth may fail to stay steady, thereby failing to obtain homogeneousnickel composite hydroxide particles that are narrow in particle sizedistribution range.

(Reaction Atmosphere in Nucleation Step)

In the nucleation step, nucleation is developed in a non-oxidizingatmosphere with an oxygen concentration of 5 volume % or less,preferably 2 volume % or less. Thus, the oxidation of cobalt isinhibited, and the production of a plate-shaped single-crystallinehydroxide is promoted to generate fine plate-shaped crystal nuclei. Asthe oxygen concentration is higher, the plate-shaped crystal nuclei tendto be thicker, and when the oxygen concentration exceeds 5 volume %,spherical or massive nuclei with fine crystals aggregated are provided,thereby failing to obtain plate-shaped crystal nuclei. As theplate-shaped crystal nuclei are thicker, the aspect ratio of thecomposite hydroxide obtained is decreased. The non-oxidizing atmosphereis considered defined by the aqueous solution during the generation ofcrystal nuclei, or the oxygen concentration in the atmosphere in contactwith the plate-shaped crystal nucleus slurry. In order to develop thecrystal nucleus into a plate shape, the oxygen concentration ispreferably adjusted to 2 volume % or less, and more preferably, theoxygen concentration is adjusted to 1 volume % or less.

(Reaction Atmosphere in Particle Growth Step)

Also in the particle growth step, the adoption of an oxidizingatmosphere may fail to achieve dense primary particles of growingplate-shaped crystal nuclei, thereby decreasing the denseness of nickelcomposite hydroxide particles obtained. Therefore, the atmosphere forthe particle growth, that is, the atmosphere in contact with the slurryfor particle growth is preferably made an atmosphere with an oxygenconcentration of 5 volume % or less, more preferably, an atmosphere withan oxygen concentration of 2 volume % or less, as with the nucleationstep.

Means for keeping the space in the reaction tank in the reactionatmosphere described above in each step includes: circulating an inertgas such as nitrogen into the space in the reaction tank; and furtherbubbling an inert gas into the reaction solution.

(Particle Size of Nickel Composite Hydroxide)

The aspect ratio of the nickel composite hydroxide produced iscorrelated with the sizes of the crystal nuclei, and can be thuscontrolled by adjusting the pH value, reaction atmosphere, stirringforce, and the like in the nucleation step. The inhibited oxidation, andthus the weakened stirring develop plate-shaped crystal nuclei, therebymaking it possible to increase the aspect ratios of primary particles,and also increase the aspect ratio of the nickel composite hydroxide. Inaddition, the development of the plate-shaped crystal nuclei canincrease plate-shaped primary particles in size.

In addition, the volume average particle size (Mv) can be controlled bythe duration of the particle growth step, and thus, when the particlegrowth step is continued until growing to a desired particle size,nickel composite hydroxide particles can be obtained which have thedesired particle size. More specifically, the above-mentionedshape-specifying values can be controlled to fall within the respectiveranges by controlling the aspect ratio in the nucleation step, andadjusting the aggregation of primary particles in the particle growthstep.

(Ammonia Concentration)

Ammonia is preferably added as a complexing agent to the slurry forparticle growth in the particle growth step. In that regard, the ammoniaconcentration in the slurry for particle growth is preferably controlledto 5 g/L to 20 g/L. The ammonia acts as a complexing agent, and thusmay, when the ammonia concentration is less than 5 g/L, fail to keep thesolubility of metal ions constant, thereby resulting in ununiformplate-shaped primary particles of plate-shaped crystal nuclei developed,and causing the nickel composite hydroxide to vary in particle size.When the ammonia concentration exceeds 20 g/L, the solubility of themetal ions may be excessively increased, thereby increasing the amountof meal ions remaining in the slurry for particle growth, and thuscausing the composition to be deviated, or the like.

In addition, when the ammonia concentration varies, the solubility ofthe metal ions will vary, thereby failing to form a uniform nickelcomposite hydroxide, and the concentration is preferably maintained at aconstant value. For example, a desired concentration is preferablymaintained, while the variation of the ammonia concentration has a rangeof an increase or a decrease on the order of 5 g/L with respect to theset concentration.

The ammonia is added with an ammonium ion supplier, but the ammonium ionsupplier is not particularly limited, and for example, ammonia, ammoniumsulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, andthe like can be used.

<1-2-3> Metal Compound Used, Reaction Condition, Etc.

Next, the metal compound (metal salt) used and the conditions such as areaction temperature will be described. It is to be noted that thedifferences in the conditions between the nucleation step and theparticle growth step are only the pH value described above, and thecontrol ranges of the compositions of the aqueous solution fornucleation and the mixed aqueous solution, and the both steps usesubstantially the same metal compound and conditions such as a reactiontemperature.

(Metal Compound)

A compound containing the intended metal is used as the metal compound.It is preferable to use a water-soluble compound for the compound used,and examples of the water-soluble compound include metal salts such asnitrates, sulfates, and hydrochlorides. For example, nickel sulfate,manganese sulfate, and cobalt sulfate are preferably used.

(Additive Element)

It is preferable to use a water-soluble compound for the additiveelement (at least one additive element selected from V, Mg, Al, Ti, Mo,Nb, Zr, and W) in the general formula (1), and for example, vanadiumsulfate, ammonium vanadate, magnesium sulfate, aluminum sulfate,titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate,zirconium sulfate, zirconium nitrate, niobium oxalate, ammoniummolybdate, sodium tungstate, ammonium tungstate, and the like can beused.

The addition of the additive element may be achieved by adding anadditive containing the additive element to the aqueous solution fornucleation or the mixed aqueous solution, thereby making coprecipitationpossible with the additive element uniformly dispersed in nickelcomposite hydroxide particles.

The additive element can be also added by coating the surface of theobtained nickel composite hydroxide with a compound containing theadditive element. Further, in the case of coating the surface with theadditive element, the ratio of the atom number of additive element ionsthat are present in the formation of the composite hydroxide bycrystallization is reduced by a coating amount, thereby making itpossible to make the ratio of the atom number of metal ions in thenickel composite hydroxide be in agreement with the final compositionratio. In addition, the step of coating the surface of the nickelcomposite hydroxide with the additive element may be applied toparticles after heating the composite hydroxide.

(Concentration of Mixed Aqueous Solution in Particle Growth Step)

The concentration of the mixed aqueous solution is preferably adjustedto 1.0 mol/L to 2.6 mol/L, preferably 1.5 mol/L to 2.2 mol/L in thetotal of the metal compound. When the concentration of the mixed aqueoussolution is less than 1.0 mol/L, productivity is unfavorably decreasedbecause of the reduced amount of the crystallization product perreaction tank.

On the other hand, when the concentration of the mixed aqueous solutionexceeds 2.6 mol/L, the concentration exceeds the saturationconcentration at normal temperature, and there is thus a risk ofclogging equipment piping due to reprecipitation of crystals.

In addition, the mixed aqueous solution does not necessarily have to besupplied to the reaction tank as a mixed aqueous solution containing allof metal compounds required for the reaction. For example, in the caseof using metal compounds that react to produce a compound when the metalcompounds are mixed, aqueous solutions of metal compounds may beprepared individually, and simultaneously supplied in predeterminedproportions as individual aqueous solutions of metal compounds into thereaction tank such that the total concentration is 1.0 mol/L to 2.6mol/L in all of the aqueous solution of metal compounds. The aqueoussolution for nucleation in the nucleation step may be also adapted as inthe case with the mixed aqueous solution.

(Reaction Solution Temperatures in Nucleation Step and Particle GrowthStep)

The solution temperature of the reaction solution during the reaction ineach step is preferably set to 20° C. or higher, particularly preferably20° C. to 70° C. When the solution temperature is less than 20° C.,nucleation is likely to be developed because of the low solubility,thereby increasing difficulty with control. In addition, fine particlesmay be generated by new nucleation in the particle growth step. On theother hand, in excess of 70° C., when ammonia is added, thevolatilization of ammonia is promoted, and an excess ammonium ionsupplier has thus to be added in order to keep a predetermined ammoniaconcentration, which leads to an increase in cost. When no ammonia isadded, the temperature is preferably adjusted to 40° C. to 70° C. inorder to make the solubility of metal ions adequate.

(Inorganic Alkaline Aqueous Solution in Nucleation Step and ParticleGrowth Step)

The inorganic alkaline aqueous solution for the adjustment of the pHvalue is not to be considered particularly limited, but for example, anaqueous solution of an alkali metal hydroxide such as sodium hydroxideand potassium hydroxide can be used. In the case of such an alkali metalhydroxide, the hydroxide may be supplied directly, but is preferablyadded as an aqueous solution, from the perspective of ease of pH controlduring crystallization.

In addition, the method for adding the inorganic alkaline aqueoussolution is not to be considered particularly limited, but the solutionmay be added with a pump capable of flow control, such as a meteringpump, such that the pH is kept in a predetermined range, whilesufficiently stirring the reaction aqueous solution and the plate-shapedcrystal nucleus slurry.

(Production Equipment)

The process for producing the nickel composite hydroxide uses a type ofapparatus that collects no product until the reaction is completed. Forexample, a batch reaction tank equipped with a stirrer is used commonly.The adoption of a type of apparatus that collects no product until thereaction is completed can provide particles that are narrow in particlesize distribution, and uniform in particle size, because the problem ofcollecting growing particles at the same time as overflow liquid is notcaused unlike continuous crystallization apparatus that collectsproducts through common overflows.

In addition, in the case of controlling the reaction atmosphere, it ispreferable to use an apparatus capable of atmosphere control, such as anairtight apparatus. The use of such an apparatus can easily providenickel composite hydroxides composed of plate-shaped secondary particleswith plate-shaped primary particles aggregated as described above.

The production process for producing the nickel composite hydroxide asdescribed above has: a nucleation step of generating plate-shapedcrystal nuclei by adjusting an aqueous solution for nucleation,including a metal compound containing cobalt, where the content ofcobalt is 90 atom % or more with respect to all metal elements, to an pHvalue of 12.5 or more on the basis of a liquid temperature of 25° C.;and a particle growth step of causing growth of the plate-shaped crystalnuclei by adjusting slurry for particle growth, containing theplate-shaped crystal nuclei formed in the nucleation step, such that thepH value of the slurry is 10.5 to 12.5 on the basis of a liquidtemperature of 25° C., and lower than the pH value in the nucleationstep, and supplying a mixed aqueous solution including a metal compoundcontaining at least nickel to the slurry for particle growth, therebymaking it possible to provide a characteristic nickel compositehydroxide as described above.

The process for producing the nickel composite hydroxide carries out thenucleation step and the particle growth step in a clearly separatedmanner, thereby making it possible to provide a characteristic nickelcomposite hydroxide as described above, and has extremely highindustrial value, due to the fact that the process is easily implementedwith high productivity, and thus suitable for production on anindustrial scale.

[2] Positive Electrode Active Material for Non-Aqueous ElectrolyteSecondary Battery and Production Process Therefor

(2-1) Positive Electrode Active Material for Non-Aqueous ElectrolyteSecondary Battery

The positive electrode active material includes a lithium-nickelcomposite hydroxide that has a hexagonal layered structure, which isrepresented by the general formula (2):Li_(1+u)Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)O₂ (in the formula, u, x, y, and zin the formula fall within ranges of: −0.05≦u≦0.50; 0<x≦0.35; 0≦y≦0.35;and 0≦z≦0.1, x, y, and z meet 0<x+y+z≦0.7, and M in the formularepresents at least one additive element selected from V, Mg, Al, Ti,Mo, Nb, Zr, and W). The positive electrode active material has thelithium-nickel composite oxide including plate-shaped secondaryparticles aggregated with overlaps between plate surfaces of multipleplate-shaped primary particles, where shapes projected from directionsperpendicular to the plate surfaces of the plate-shaped primaryparticles are any plane projection shape of spherical, elliptical,oblong, and massive shapes, and the secondary particles have an aspectratio of 3 to 20, and a volume average particle size (Mv) of 4 μm to 20μm measured by a laser diffraction scattering method.

The adoption of the composition as mentioned above can provide superiorperformance as a positive electrode active material for a non-aqueouselectrolyte secondary battery. In addition, this positive electrodeactive material is composed of the plate-shaped secondary particlesaggregated with overlaps between the plate surfaces of the multipleplate-shaped primary particles of the lithium-nickel composite oxide,thus making it possible to achieve the increased area of contact with anelectrolytic solution, and a high filling density because of the plateshape. Thus, when this positive electrode active material is used for apositive electrode of a battery, high output characteristics and batterycapacity are achieved, thereby making it possible to achieve a highelectrode density.

(Composition)

In the positive electrode active material, u indicating the excessiveamount of lithium meets −0.05≦u≦0.50. When the excessive amount u oflithium is less than −0.05, that is, the content of lithium is lowerthan 0.95, the reaction resistance of a positive electrode will beincreased in a non-aqueous electrolyte secondary battery that uses thepositive electrode active material obtained, thereby decreasing theoutput of the battery.

On the other hand, when the excessive amount u of lithium exceeds 0.50,that is, the content of lithium is higher than 1.50, the initialdischarge capacity will be decreased in the case of using the positiveelectrode active material for a positive electrode of a battery, and thereaction resistance of the positive electrode will be also increased.The excessive amount u of lithium is preferably adjusted to 0.10 ormore, and preferably adjusted to 0.35 or less in order to further reducethe reaction resistance.

x indicating the content of cobalt meets 0<x≦0.35. Cobalt is an additiveelement that contributes to improved cycle characteristics. When thevalue of x exceeds 0.35, the initial discharge capacity will bedecreased significantly. As described above, the nickel compositehydroxide as a precursor for use in the production of the positiveelectrode active material is developed from plate-shaped crystal nucleiof a hydroxide containing at least cobalt, and x thus meets 0<x,preferably 0.05≦x≦0.35, more preferably 0.1≦x≦0.35.

y indicating the content of manganese meets 0≦y≦0.35. Manganese is anadditive element that contributes to improved thermal stability. Whenthe value of y exceeds 0.35, characteristic degradation will be caused,because of manganese eluted into an electrolytic solution in storage athigh temperatures or in battery operation.

As expressed by the general formula (2), the positive electrode activematerial is more preferably adjusted such that the lithium-nickelcomposite oxide contains therein the additive element. Containing theadditive element can improve durability and output characteristics of abattery that uses the oxide as a positive electrode active material. Inparticular, the additive element uniformly distributed on the surfacesof particles or in the particles allows the whole particles to achievethe advantageous effects, and the addition of small amount of theelement can achieve the advantageous effects, and keep the capacity frombeing decreased.

When the atom ratio z of the additive element M to the total number ofatoms exceeds 0.1, the battery capacity is unfavorably decreased becauseof the decreased amount of a metal element that contributes to a Redoxreaction. Accordingly, the atom ratio of the additive element M isadjusted to fall within the range of 0≦z≦0.1.

(Particle Shape and Structure)

The positive electrode active material uses the nickel compositehydroxide composed of plate-shaped secondary particles aggregated withoverlaps between plate surfaces of multiple plate-shaped primaryparticles of the above-described nickel composite hydroxide as aprecursor, where the shapes projected from directions perpendicular toplate surfaces of the plate-shaped primary particles are any planeprojection shape of circular, elliptical, oblong, and potato-likemassive shapes. Accordingly, the positive electrode active material hasa similar particle structure to the nickel composite hydroxide.

In the positive electrode active material that has this structure, thesurfaces of primary particles in secondary particles also havesufficient voids generated as in the case with the nickel compositehydroxide. Accordingly, the specific surface area is increased ascompared with common plate-shaped particles composed of plate-shapedsecondary particles formed as polycrystalline bodies of primaryparticles. In addition, each individual primary particle has a smallparticle size, thus making it easy to insert and extract lithium, andthus increasing the insertion and extraction rates. Furthermore, thesecondary particles are formed from constituent particles with primaryparticles aggregated, thus making it possible to deliver an electrolytesufficiently in the secondary particles, and lithium is inserted andextracted at voids and grain boundaries present between the primaryparticles. These advantageous effects bring output characteristics closeto those in the case of particles that are small in particle size,thereby making a more significant improvement than in the case ofplate-shaped particles.

On the other hand, because the individual secondary particles aggregatewith overlaps between plate surfaces, thereby growing two-dimensionally,filling with the secondary particles oriented in electrode preparationcan reduce the gaps between the particles, which are found in the caseof filling with particles that are small in particle size, therebymaking it possible to achieve a high filing density, and thus achievinga high volume energy density. In addition, it also becomes possible tomake the electrode a thin film. Accordingly, the use of the positiveelectrode active material composed of plate-shaped secondary particleswith a plurality of plate-shaped primary particles of the nickelcomposite hydroxide aggregated with overlaps between plate surfaces asdescribed above makes it possible to achieve a balance between highoutput characteristics and battery capacity, and a high electrodedensity.

The secondary particles of the positive electrode active material havean aspect ratio of 3 to 20, and the positive electrode active materialhas a volume average particle size (Mv) of 4 μm to 20 μm measured by alaser diffraction scattering method.

When the aspect ratio is less than 3, flatness of the plate shape isdecreased, and results in failure to achieve a high filling density withparticles oriented in electrode preparation. In addition, the resistanceincreased against diffusion of lithium into particles will degradeoutput characteristics. On the other hand, when the aspect ratio exceeds20, the decreased particle strength of the secondary particles willresult in easily broken particles in kneading slurry for electrodepreparation, thereby insufficiently producing the effect of the plateshape. In addition, the filling density for the electrode will be alsodecreased, thereby decreasing the volume energy density.

The volume average particle size (Mv) of less than 4 μm will increasegaps between secondary particles in filling even when the particles havea plate shape, thus decreasing the volume energy density. In addition,the viscosity will be increased in kneading slurry for electrodepreparation, thereby causing a decrease in handling ability. The volumeaverage particle size (Mv) in excess of 20 μm will cause lineation inthe preparation of an electrode film, and a short circuit through aseparator. The volume average particle size (Mv) in the range of 4 μm to20 μm can provide a positive electrode active material which provides anelectrode with a high volume energy density, and suppresses lineation inthe preparation of an electrode film and a short circuit through aseparator.

Furthermore, in the positive electrode active material, the averagevalue is preferably 1 to 5 μm for the maximum diameters of shapesprojected from directions perpendicular to plate surfaces ofplate-shaped primary particles (the maximum diameters of plate-shapedprimary particles projected from directions perpendicular to platesurfaces of secondary particles). Thus, because lithium is inserted andextracted at voids and grain boundaries present between the plate-shapedprimary particles, output characteristics are brought close to those inthe case of particles that are small in particle size, thereby making amore significant improvement than in the case of plate-shaped particles.When the average value is less than 1 μm for the maximum diameters ofthe plate-shaped primary particles, the gaps between the plate-shapedprimary particles will be excessively increased, thereby decreasing thedenseness of the secondary particles, and an insufficient fillingdensity may be achieved. On the other hand, when the average value forthe maximum diameters exceeds 5 μm, such advantageous effects may beachieved insufficiently, which are achieved in the case of filling withparticles that are small in particle size. The shape-specifying values(aspect ratio, Mv) and the average value for the maximum diameters ofthe plate-shaped primary particles can be obtained in the same way asthe nickel composite hydroxide to serve as a precursor.

(Specific Surface Area)

The positive electrode active material preferably has a specific surfacearea of 0.3 m²/g to 2 m²/g. When the specific surface area is less than0.3 m²/g, the contact with an electrolytic solution may be achievedinsufficiently, thereby resulting in degraded output characteristics andbattery capacity. Alternatively, when the specific surface area exceeds2 m²/g, the decomposition of an electrolytic solution may beaccelerated, thereby resulting in safety deterioration, or causinghigh-temperature storage stability to be decreased by manganese elutionwhen manganese is added. The adjustment of the specific surface area to0.3 m²/g to 2 m²/g achieves favorable battery characteristics, and canalso ensure safety and high-temperature storage stability.

(Particle Size Distribution)

The positive electrode active material is preferably 0.75 or less in[(D90−D10)/Mv] indicating a particle size variation index, which iscalculated from D90 and D10 in a particle size distribution obtained bya laser diffraction scattering method and the volume average particlesize (Mv).

When the positive electrode active material has a wide particle sizedistribution, the positive electrode active material is supposed to havemany fine particles that are very small in particle size with respect tothe average particle size, and many coarse particles that are very largein particle size with respect to the average particle size. When apositive electrode is formed with the use of a positive electrode activematerial that has many fine particles, there is a possibility of heatgeneration due to local reactions between the fine particles, the fineparticles are likely to undergo selective degradation, with safetydeterioration, and cycle characteristics may be thus worsened. On theother hand, when a positive electrode is formed with the use of apositive electrode active material that has many coarse particles, thecoarse particles decrease the area of a reaction between a electrolyticsolution and the positive electrode active material, and the batteryoutput may be thus decreased by an increase in reaction resistance. Whenthe variation index is lower, the positive electrode active material canbe improved in property, but the variation index has a realistic lowerlimit on the order of 0.30 according to the present invention.

Accordingly, the particle size distribution of the positive electrodeactive material is adjusted to 0.75 or less in [(D90−D10)/Mv] indicatingthe particle size variation index, thereby making it possible to reducethe proportions of fine particles and coarse particles. The battery thatuses the foregoing positive electrode active material for a positiveelectrode is further excellent in safety, and adapted to have morefavorable cycle characteristics and battery output. It is to be notedthat the average particle size, and D90 and D10 are specified as in thecase of the composite hydroxide particles described above, and themeasurement method therefor can be also adopted in the same way.

Furthermore, the positive electrode active material preferably has asite occupancy of 7% or less at 3 a sites with metal ions other thanlithium, and a site occupancy of 7% or less at 3 b sites with lithiumions, which are obtained from Rietveld analysis with X-ray diffractionanalysis. The site occupancies at the 3 a sites and the 3 b sites beyondthe foregoing range indicate that the lithium-nickel composite oxide isbrought into cation mixing, with low crystallinity. In the case of lowcrystallinity, the metal ions at the 3 a sites significantly interferewith movement of lithium ions, and deactivation of the lithium ions atthe 3 b sites has significant influence, which may degrade batterycharacteristics, in particular, charge-discharge capacity or outputcharacteristics.

In addition, the positive electrode active material preferably has anorientation index of 0.9 to 1.1 at the (003) plane, which is found byX-ray diffraction analysis. This orientation index presented means thatcrystals are arranged in a non-orientation and random manner. Thenon-orientation of crystals can achieve a balance between batterycapacity and output characteristics affected by the insertion-extractionability of lithium, and cycle characteristics and safety affected bydurability of the layered structure. The deviation of the orientationindex at the (003) plane to either side may result in failure to achievea balance between the characteristics required as a battery in highdimensions, thereby insufficiently achieving any of the batterycharacteristics.

In addition, this lithium-nickel composite oxide is composed ofsecondary particles where spherical or massive lithium-nickel compositeoxide particles formed by the aggregation of primary particles areconnected in two-dimensional directions, thus making it possible toachieve the increased area of contact with an electrolytic solution, anda high filling density because of the plate shape. Therefore, when thislithium-nickel composite oxide is used as a positive electrode activematerial, high output characteristics and battery capacity are achieved,thereby making it possible to achieve a high electrode density.

The positive electrode active material as described above has thelithium-nickel composite oxide characteristically including plate-shapedsecondary particles aggregated with overlaps between plate surfaces ofmultiple plate-shaped primary particles, where the shapes projected fromdirections perpendicular to the plate surfaces of the plate-shapedprimary particles are any plane projection shape of spherical,elliptical, oblong, and massive shapes, and the secondary particles havean aspect ratio of 3 to 20, and a volume average particle size (Mv) of 4μm to 20 μm measured by a laser diffraction scattering method.

The positive electrode active material is produced from the nickelcomposite hydroxide which is characteristic as described above and alithium compound, and thus adapted to take over the composition andproperties of the nickel composite hydroxide. Accordingly, the foregoingpositive electrode active material increases the area of contact with anelectrolytic solution, and produces an increased filling density for apositive electrode. As a result, with the positive electrode activematerial as described above, thin electrode films can be formed, andnon-aqueous electrolyte secondary batteries can be obtained whichachieve high output characteristics and battery capacity and has a highelectrode density.

(2-2) Process for Producing Positive Electrode Active Material forNon-Aqueous Electrolyte Secondary Battery

The process for producing the positive electrode active material atleast includes: a mixing step of forming a mixture by mixing a lithiumcompound with the nickel composite hydroxide described above; and acalcining step of calcining the mixture formed in the mixing step.

The process for producing the positive electrode active material is notparticularly limited as long as the positive electrode active materialcan be produced such that the secondary particles have a shape, astructure, and a composition as described above, but it is preferable toadopt the following method because the positive electrode activematerial can be produced more reliably. The respective steps will bedescribed below.

(a) Heat Treatment Step

First, the nickel composite hydroxide prepared in the way describedabove is subjected to a heat treatment, if necessary.

The heat treatment step is a step of heating the nickel compositehydroxide to a temperature of 300° C. to 750° C. in an oxidizingatmosphere, thereby carrying out a heat treatment, which removes watercontained in the nickel composite hydroxide. This heat treatment step iscarried out, thereby making it possible to reduce water in theparticles, remaining up to the calcining step, down to a certain amountof water. Thus, the positive electrode active material produced can beprevented from varying in the ratio of the metal atom number or lithiumatom number in the material. Accordingly, this step can be skipped aslong as the ratio between the metal atom number and the lithium atomnumber in the positive electrode active material can be controlledprecisely.

In the heat treatment step, water has only to be able to be removedwithout varying in the ratio between the metal atom number and thelithium atom number in the positive electrode active material, and thus,the nickel composite hydroxide does not necessarily have to be allconverted to a nickel composite oxide. However, in order to furtherreduce the variation in the ratio between the atom numbers, the nickelcomposite hydroxide is preferably all converted to a nickel compositeoxide with the heating temperature adjusted to 500° C. or higher.

In the heat treatment step, when the heating temperature is lower than300° C., excess water in the nickel composite hydroxide can be removedinsufficiently, and the ratio between the atom numbers may be keptinsufficiently from varying. On the other hand, when the heatingtemperature exceeds 750° C., the heat treatment may make the particlesbe sintered, thereby resulting in failure to obtain any nickel compositeoxide that is uniform in particle size. The ratio between the atomnumbers can be kept from varying, in a way that the metal componentcontained in the nickel composite hydroxide under the heat treatmentcondition is found in advance by analysis, thereby determining the ratiobetween the metal component and the lithium compound.

The atmosphere in which the heat treatment is carried out is not to beconsidered particularly limited, but has only to be an atmosphere thatis not reduced, that is, a non-reducing atmosphere, and the heattreatment is preferably carried out in an oxidizing atmosphere, inparticular, in an air flow where the heat treatment is carried out in asimplified manner.

In addition, the heat treatment time is not particularly limited, butpreferably at least 1 hour or more, more preferably 5 hours to 15 hours,because excess water in the nickel composite hydroxide may be removedinsufficiently for shorter than 1 hour.

Further, the equipment for use in the heat treatment is not to beconsidered particularly limited, but may be any equipment as long as theequipment can heat the nickel composite hydroxide in a non-reducingatmosphere, preferably in an air flow, and an electric furnace withoutgas generation or the like is used in a preferred manner.

(b) Mixing Step

The mixing step is a step of mixing the nickel composite hydroxide orthe nickel composite hydroxide subjected to the heat treatment in theheat treatment step (hereinafter, referred to as “heat-treatedparticles”) with a lithium compound, thereby providing a lithiummixture.

In this regard, the heat-treated particles include not only the nickelcomposite hydroxide with residual water removed therefrom in the heattreatment step, but also the nickel composite hydroxide converted to anoxide in the heat treatment step, or mixed particles.

The nickel composite hydroxide or heat-treated particles and the lithiumcompound are mixed such that the ratio (Li/Me) of the lithium atomnumber (Li) to the atom number of metals other than lithium, that is,the sum (Me) of the atom numbers of nickel, manganese, cobalt, and theadditive element M in the lithium mixture is 0.95 to 1.5, preferably 1to 1.5, more preferably 1 to 1.35. More specifically, the Li/Me ofmixing in the mixing step corresponds to the Li/Me in the positiveelectrode active material because the Li/Me is not changed betweenbefore and after the calcining step, and the mixing is carried out suchthat the Li/Me in the lithium mixture is equal to the Li/Me in thepositive electrode active material to be obtained.

The lithium compound used for forming the lithium mixture is not to beconsidered particularly limited, but for example, lithium hydroxide,lithium nitrate, lithium carbonate, or mixtures thereof are preferred interms of being easily available. In particular, in consideration of easeof handling and quality stability, it is more preferable to use lithiumhydroxide or lithium carbonate.

It is to be noted that the lithium mixture is preferably mixedsufficiently before the calcination. In the case of insufficient mixing,there is a possibility that the Li/Me will vary among individualparticles, thereby causing problems such as failure to achieve adequatebattery characteristics.

In addition, for the mixing, common mixing machines can be used, and forexample, shaker mixers, Loedige mixers, Julia mixers, and V blenders canbe used. The mixing has only to mix the nickel composite hydroxide andthe heat-treated particles sufficiently with the lithium compound, tothe extent that the nickel composite hydroxide or heat-treated particlesare not broken in shape.

(c) Calcining Step

The calcining step is a step of calcining the lithium mixture obtainedin the mixing step, thereby forming a lithium-nickel composite oxide.Calcining the lithium mixture in the calcining step diffuses the lithiumin the lithium compound into the nickel composite hydroxide and theheat-treated particles, thus forming lithium-nickel composite oxideparticles. In addition, even when the nickel composite hydroxide has ahigh concentration layer of cobalt, the diffusion causes the highconcentration layer to disappear, thereby eliminating the presence ofstructural layered products.

(Calcination Temperature)

The lithium mixture is calcined at 650° C. to 980° C., more preferably750° C. to 950° C. The calcination temperature of lower than 650° C.insufficiently diffuses lithium into the nickel composite hydroxide andthe heat-treated particles, thereby leaving excess lithium or unreactedparticles, or insufficiently completing crystal structures, and adequatebattery characteristics thus fail to be achieved in the case of use in abattery. Alternatively, there is a possibility that the calcinationtemperature in excess of 980° C. will cause intense sintering betweenparticles of the lithium-nickel composite oxide, and cause abnormalparticle growth, and for this reason, there is a possibility thatcalcined particles will be coarse, thereby resulting in an inability tomaintain the particle shapes of secondary particles as described above.Such a positive electrode active material fails to achieve theadvantageous effect of the secondary particle shape as described above.

It is to be noted that from the perspective of homogeneously developingthe reaction of the nickel composite hydroxide and the heat-treatedparticles with the lithium compound, it is preferable to increase intemperature up to the calcination temperature at a rate of temperatureincrease from 3° C./min to 10° C./min. Furthermore, keeping atemperature around the melting point of the lithium compound for 1 hourto 5 hours can develop the reaction in a more homogeneous manner.

(Calcining Time)

The holding time at the calcination temperature in the calcining time ispreferably at least 2 hours or more, more preferably 4 hours to 24hours. The holding time of shorter than 2 hours may make thecrystallinity of the lithium-nickel composite oxide insufficient. In thecase of calcining a sagger filled with the lithium mixture after theholding time, which is not to be considered particularly limited, it ispreferable to cool the atmosphere at a rate of temperature decrease from2° C./imin to 10° C./min until reaching 200° C. or lower in order toprevent the sagger from being deteriorated.

(Pre-Calcination)

In particular, when lithium hydroxide or lithium carbonate is used asthe lithium compound, the mixture is preferably subjected topre-calcination before the calcination by keeping the compound at atemperature that is lower than the calcination temperature and 350° C.to 800° C., preferably 450° C. to 780° C. for approximately 1 hour to 10hours, preferably 3 hours to 6 hours. More specifically, the mixture ispreferably subjected to pre-calcination at the temperature of thereaction between the lithium hydroxide or lithium carbonate and thenickel composite hydroxide and heat-treated particles. In this case,keeping the mixture around the reaction temperature of the lithiumhydroxide or lithium carbonate sufficiently diffuses lithium into thenickel composite hydroxide and the heat-treated particles, therebymaking it possible to provide a homogeneous lithium-nickel compositeoxide.

(Calcination Atmosphere)

The atmosphere for the calcination is an oxidizing atmosphere, theoxygen concentration is preferably adjusted to 18 volume % to 100 volume%, and a mixed atmosphere of oxygen and an inert gas is more preferred.More specifically, the calcination is preferably carried out in the airatmosphere, or in an oxygen flow. When the oxygen concentration is lowerthan 18 volume %, there is a possibility that the crystallinity of thelithium-nickel composite oxide will be insufficient.

It is to be noted that the furnace for use in the calcination is not tobe considered particularly limited, as long as the furnace can heat thelithium mixture in the air atmosphere or an oxygen flow, but from theperspective of keeping the atmosphere in the furnace homogeneous, anelectric furnace without gas generation is preferred, and any batch orcontinuous furnace can be used.

(Grinding)

The lithium-nickel composite oxide obtained by the calcination may beaggregated, or lightly sintered. In this case, the oxide may besubjected to grinding, thereby making it possible to provide alithium-nickel composite oxide, that is, a positive electrode activematerial according to the present embodiment.

It is to be noted that the grinding refers to the operation of inputtingmechanical energy to aggregates composed of multiple secondary particlesproduced by sintering necking or the like between secondary particlesduring the calcination, thereby separating the secondary particlesalmost without destroying the secondary particles themselves, thusloosening the aggregates. This operation can provide a lithium-nickelcomposite oxide with a narrow particle size distribution, while thesecondary particle structure is kept.

The process for producing the positive electrode active material asdescribed above includes: the mixing step of mixing the nickel compositehydroxide with the lithium compound, thereby forming the lithiummixture; and the calcining step of calcining the lithium mixture formedin the mixing step at a temperature of 650° C. to 980° C. in anoxidizing atmosphere, thereby making it possible to provide a positiveelectrode active material which is characteristic as described above.

The process for producing the positive electrode active material hasextremely high industrial value, due to the fact that the process iseasily implemented with high productivity, and thus suitable forproduction on an industrial scale.

[3] Non-Aqueous Electrolyte Secondary Battery

The non-aqueous electrolyte secondary battery adopts a positiveelectrode that uses the positive electrode active material describedabove. First, the structure of the non-aqueous electrolyte secondarybattery will be described.

The non-aqueous electrolyte secondary battery (hereinafter, referred tosimply as a “secondary battery”) according to the present embodiment hassubstantially the same structure as a common non-aqueous electrolytesecondary battery, except for the use of the positive electrode activematerial described above for a positive electrode material, and thuswill be described briefly.

The secondary battery may have a known common configuration such ascylindrical, rectangular, coin, and button shape. For example, in thecase of a cylindrical secondary battery, the secondary battery has acase, and a structure including a positive electrode, a negativeelectrode, a non-aqueous electrolyte, and a separator housed in thecase. More specifically, the secondary battery is formed by stacking thepositive electrode and the negative electrode with the separatorinterposed therebetween, thereby providing an electrode body,impregnating the obtained electrode body with the non-aqueouselectrolyte, making connections between a positive electrode currentcollector of the positive electrode and a positive electrode terminalleading to the exterior, and between a negative electrode currentcollector of the negative electrode and a negative electrode terminalleading to the exterior, respectively with the use of leads for currentcollection or the like, and sealing the body in the case.

It is to be noted that the structure of the secondary battery to whichthe present invention can be applied is obviously not limited to theexample mentioned above, and as for the outline of the battery, variousshapes can be adopted such as a cylindrical and stacked shape.

(Positive Electrode)

The positive electrode is a sheet-like member, which can be formed in away that a positive electrode mixture paste containing the positiveelectrode active material is applied to the surface of a currentcollector, for example, made of aluminum foil, and dried. In addition,the positive electrode mixture paste applied to the surface of a currentcollector and dried may be referred to as an “electrode film”.

Further, the positive electrode is processed appropriately in accordancewith a battery that uses the positive electrode. The positive electrodeis subjected to, for example, cutting for forming into an appropriatesize depending on the intended battery, or pressure compression througha roll press or the like in order to increase the electrode density.

The positive electrode mixture paste is formed by kneading with theaddition of a solvent to a positive electrode mixture. The positiveelectrode mixture is formed by mixing the powdery positive electrodeactive material according to the present invention with a conductivematerial and a binder.

The conductive material is added for providing the electrode withappropriate conductivity. This conductive material is not particularlylimited, but for example, carbon black materials can be used such asgraphite (e.g., natural graphite, artificial graphite, and expandedgraphite), acetylene black, and Ketjen black.

The binder serves to bind positive electrode active material particlestogether. The binder for use in the positive electrode mixture is notparticularly limited, but for example, polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), fluorine-containing rubbers,ethylene-propylene-diene rubbers, styrene butadiene, cellulose resins,and polyacrylic acid can be used.

Further, activated carbon or the like may be added to the positiveelectrode mixture, and the addition of activated carbon or the like canincrease the electric double layer capacity of the positive electrode.

The solvent dissolves the binder, and diffuses the positive electrodeactive material, the conductive material, and the activated carbon orthe like in the binder. This solvent is not particularly limited, butfor example, organic solvents such as N-methyl-2-pyrrolidone can beused.

In addition, the mixture proportions of the respective substances arenot particularly limited in the positive electrode mixture paste. Forexample, when the solid content of the positive electrode mixtureexcluding the solvent is regarded as 100 parts by mass, the mixtureproportions may be the same as those in a positive electrode of a commonnon-aqueous electrolyte secondary battery, the content of the positiveelectrode active material can be 60 parts by mass to 95 parts by mass,the content of the conductive material can be 1 part by mass to 20 partsby mass, and the content of the binder can be 1 part by mass to 20 partsby mass.

(Negative Electrode)

The negative electrode is a sheet-like member formed by applying anegative electrode mixture paste to the surface of a current collectorof metal foil such as copper, and dying the paste. While this negativeelectrode differs in the constituents of the negative electrode mixturepaste, the combination of the constituents, the material of the currentcollector, and the like, the negative electrode is formed substantiallyin the same way as the positive electrode, and subjected to varioustypes of processing, if necessary, as with the positive electrode.

The negative electrode mixture paste is obtained in a way that anappropriate solvent is added to a negative electrode mixture obtained bymixing a negative electrode active material and a binder, thereby makinga paste.

The negative electrode active material can adopt, for example, alithium-containing substance such as metal lithium and a lithium alloy,or an occlusion substance that can occlude and desorb lithium ions.

The occlusion substance is not particularly limited, but for example,calcined products of organic compounds such as natural graphite,artificial graphite, and phenolic resins, and powdery products ofcarbonaceous substances such as coke can be used. When the occlusionsubstance is adopted for the negative electrode active material, as withthe positive electrode, a fluorine-containing resin such as PVDF can beused as a binder, and an organic solvent such as N-methyl-2-pyrrolidonecan be used as a solvent for dispersion of the negative electrode activematerial in the binder.

(Separator)

The separator is disposed to be sandwiched between the positiveelectrode and the negative electrode, and has the functions ofseparating the positive electrode and the negative electrode and holdingthe electrolyte. This separator can use, for example, a thin film suchas polyethylene and polypropylene, which has a large number ofmicropores. It is to be noted that the separator is not particularlylimited as long as the separator has the separator functions.

(Non-Aqueous Electrolyte)

The non-aqueous electrolyte is a lithium salt as a supporting salt,dissolved in an organic solvent. As the organic solvent, one selectedfrom cyclic carbonates such as ethylene carbonate, propylene carbonate,butylene carbonate, and trifluoropropylene carbonate; chain carbonatessuch as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate,and dipropyl carbonate; ether compounds such as tetrahydrofuran,2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such asethyl methyl sulfone and butanesultone; and phosphorous compound such astriethyl phosphate and trioctyl phosphate can be used singly, or two ormore thereof can be used in mixture.

LiPF₆, LiBF₄, LiClO₄, LiAsF₆, LiN(CF₃SO₂)₂, and composite salts thereofcan be used as the supporting salt.

It is to be noted that the electrolytic solution may include a radicalscavenger, a surfactant, a flame retardant, and the like for theimprovement of battery characteristics.

(Battery Characteristics of Non-Aqueous Electrolyte Secondary Battery)

The secondary battery that has the configuration described above has thepositive electrode that uses the positive electrode active material thathas characteristic structure and properties as described above, thus hasan increased area of contact between the positive electrode activematerial and the non-aqueous electrolyte, and an increased density offilling with the positive electrode active material, thereby achievinghigh output characteristics and battery capacity, and thus making itpossible to achieve a high electrode density, in spite of the thinelectrode film. Therefore, the secondary battery allows the formation ofa thin electrode film, thereby achieving a high initial dischargecapacity and a low positive electrode resistance, and thus resulting ina high output with a high capacity. In addition, the secondary batteryhas a high volume energy density. Furthermore, the thermal stability ishigh, and the safety is also excellent, as compared with conventionalpositive electrode active materials of lithium-nickel oxides.

(Applications of Secondary Battery)

The secondary battery is, because the battery has excellent batterycharacteristics, preferred for a power source of a small portableelectronic device (e.g., lap-top personal computer, a cellular phoneunit) which always requires a high capacity.

In addition, the secondary battery is also preferred for a battery as apower source for motor drive, which requires a high output. In general,the increase in battery size makes it difficult to ensure safety,thereby making an expensive protective circuit essential. However, thesecondary battery has excellent safety performance, thereby not onlymaking it easy to ensure safety, but also making it possible to simplifyan expensive protective circuit, and thus further reduce the cost.Further, it is possible to reduce the size of the secondary battery, andincrease the output thereof, and the secondary battery is thus preferredas a power source for a transportation device subjected to a restrictionon mounting space.

EXAMPLES

The present invention will be described in more detail below withreference to examples and comparative examples, but the presentinvention is not to be considered limited by the examples in any way.Evaluations on the present examples were made in the following way. Itis to be noted that unless otherwise noted, respective samples ofspecial grade chemicals from Wako Pure Chemical Industries, Ltd. wereused for the production of the lithium-nickel composite oxide andpositive electrode active material and the production of the secondarybattery.

(1) Volume Average Particle Size and Particle Size DistributionMeasurement

Evaluations were made from the results of measurement with a laserdiffraction type particle size analyzer (trade name: Microtrac fromNIKKISO CO., LTD.).

(2) Appearance of Particle

Observations were made with a scanning electron microscope (SEM(Scanning Electron Microscope): trade name S-4700 from HitachiHigh-Technologies Corporation). For the aspect ratio, twenty particleswere selected in a random manner and subjected to the measurement in theSEM observation, and the average value was calculated. For the averagevalue for the maximum diameters of plate-shaped primary particles, fiftyparticles were selected in a random manner and subjected to themeasurement in the SEM observation, and the average value wascalculated.

(3) Analysis of Metal Component

The sample was dissolved, and then confirmed by an ICP (InductivelyCoupled Plasma) emission spectrometry.

(4) Preparation and Evaluation of Battery

(Evaluation Battery)

Used was the 2032 type coin battery (hereinafter, referred to as a“coin-type battery 1”) shown in FIG. 4. As shown in FIG. 4, thecoin-type battery 1 is composed of a case 2 and an electrode 3 housed inthe case 2. The case 2 has a positive electrode can 2 a that is hollowand opened at one end, and a negative electrode can 2 b disposed at theopening of the positive electrode can 2 a, and the case is configuredsuch that a space that houses the electrode 3 is formed between thenegative electrode can 2 b and the positive electrode can 2 a when thenegative electrode can 2 b is disposed at the opening of the positiveelectrode can 2 a. The electrode 3 is composed of a positive electrode 3a, a separator 3 c, and a negative electrode 3 b, stacked to be arrangedin this order, and housed in the case 2 such that the positive electrode3 a is brought into contact with the inner surface of the positiveelectrode can 2 a, whereas the negative electrode 3 b is brought intocontact with the inner surface of the negative electrode can 2 b.Further, the case 2 includes a gasket 2 c, and the gasket 2 c fixesrelative movements such that the positive electrode can 2 a and thenegative electrode can 2 b are kept without making contact with eachother. In addition, the gasket 2 c also has the function of hermeticallysealing the gap between the positive electrode can 2 a and the negativeelectrode can 2 b, and thus isolating the inside of the case 2 from theoutside in an airtight and liquid-tight manner.

(Preparation of Battery)

First, 52.5 mg of the positive electrode active material, 15 mg ofacetylene black, and 7.5 mg of a polytetrafluoroethylene resin (PTFE)were mixed, and pressed into a shape of 11 mm in diameter and 100 μm inthickness at a pressure of 100 MPa, thereby preparing the positiveelectrode 3 a. The prepared positive electrode 3 a was dried for 12hours at 120° C. in a vacuum drier. The positive electrode 3 a, thenegative electrode 3 b, the separator 3 c, and an electrolytic solutionwere used to prepare the above-mentioned coin-type battery 1 in a glovebox in an Ar atmosphere with a dew point controlled at −80° C. Further,for the negative electrode 3 b, a negative electrode sheet punched intoa disc-like shape of 14 mm in diameter was used with a graphite powderon the order of 20 μm in average particle size and polyvinylidenefluoride applied to copper foil. In addition, a polyethylene porous filmof 25 μm in film thickness was used for the separator 3 c. For theelectrolytic solution, a mixed solution of equal parts of ethylenecarbonate (EC) and diethyl carbonate (DEC) with 1 M of LiClO₄ as asupporting electrolyte (from TOMIYAMA PURE CHEMICAL INDUSTRIES, Ltd.)was used.

(Initial Discharge Capacity)

When the coin-type battery 1 prepared was left for approximately 24hours, charged to a cutoff voltage of 4.3 V with a current densityadjusted to 0.1 mA/cm² for the positive electrode 3 a after the opencircuit voltage OCV (Open Circuit Voltage) was stabilized, anddischarged to a cutoff voltage of 3.0 V after a pause for 1 hour, thecapacity was regarded as an initial discharge capacity.

(Cycle Capacity Maintenance Rate)

With a current density adjusted to 2 mA/cm² for the positive electrodeof the coin-type battery 1, the cycle of charging up to 4.2 V anddischarging down to 3.0 V was repeated 200 times, and the ratio betweenthe discharge capacity after the repetition of charge and discharge andthe initial discharge capacity was calculated as a cycle capacitymaintenance rate. A multichannel voltage/current generator (fromADVANTEST CORPORATION, R6741A) was used for the measurement of thecharge-discharge capacity.

(Rate Characteristics)

Evaluations were made from the discharge capacity maintenance rate ofthe coin-type battery 1 in the case of the discharge rate increased from0.2 C to 5 C.

Example 1

[Nucleation Step]

According to Example 1, cobalt (II) sulfate heptahydrate (Co molarconcentration: 1.38 mol/L) and 900 mL of pure water were put in acrystallization reaction container of 5 L in volume equipped with fourbaffle plates, and warmed to 60° C. in a thermostatic tank and a warmingjacket while stirring at a revolving speed of 1000 rpm with six inclinedblade paddles, thereby providing an unreacted aqueous solution. Anitrogen gas was distributed in the reaction container, therebyproviding a nitrogen atmosphere therein, and the oxygen concentrationwas 1.0% in the space in the reaction rank in this case. An aqueoussolution of 6.25 mass % sodium hydroxide was supplied at 42 mL/min toincrease the pH of the unreacted aqueous solution up to 13 on the basisof a liquid temperature of 25° C., and then stirred continuously for 30minutes, thereby providing plate-shaped crystal nucleus-containingslurry.

[Particle Growth Step]

According to Example 1, an aqueous solution including a nickel sulfate(Ni molar concentration: 1.25 mol/L) and a manganese sulfate (Mn molarconcentration: 0.75 mol/L) was prepared as the mixed aqueous solution.To the plate-shaped nucleus-containing slurry, 25 mass % ammonia waterwas added such that the ammonia concentration in the tank was 10 g/L,and an aqueous solution of 64 mass % sulfuric acid was further addedthereto to adjust the pH to 11.6 on the basis of a liquid temperature of25° C., thereby providing slurry for particle growth. As with thenucleation step, in a nitrogen atmosphere, the mixed aqueous solutionwas supplied at 12.9 ml/min to the slurry for particle growth, and inaddition, an aqueous solution of 25 mass % sodium hydroxide was suppliedthereto while supplying 25 mass % ammonia water as a complexing agent,thereby controlling the slurry such that the ammonia concentration was10 g/L with constant pH of 11.6 on the basis of a liquid temperature of25° C., and thus producing a nickel composite hydroxide. Thereafter, thehydroxide was washed with water, filtrated, and dried for 24 hours at120° C. in the air atmosphere. The nickel composite hydroxide obtainedwas Ni_(0.50)Co_(0.20)Mn_(0.30)(OH)₂ in composition. In addition, thevolume average particle size (Mv) was 10.6 μm, and the [(D90−D10)/Mv]indicating a particle size variation index was 0.65.

FIG. 5 shows a SEM observation result in Example 1. The aspect ratiomeasured from the SEM observation was 6.3, and the average value was 2.1μm for the maximum diameters of shapes projected from directionsperpendicular to plate surfaces of plate-shaped primary particles (themaximum diameters of plate-shaped primary particles projected fromdirections perpendicular to plate surfaces of secondary particles). Theanalysis of a cross section of the obtained nickel composite hydroxide(secondary particles) with an energy dispersive X-ray analyzer confirmedthat a high concentration layer containing cobalt was formed in centralparts of the secondary particles in the width directions thereof, andthe high concentration layer was 0.4 μm in average thickness.

[Production and Evaluation of Positive Electrode Active Material]

According to Example 1, the obtained nickel composite hydroxide andlithium hydroxide weighed to meet Li/Me=1.02 were mixed to form alithium mixture. The mixing was carried out with the use of ashaker-mixer (from Willy A. Bachofen AG (WAB), TURBULA Typet2C).

Next, according to Example 1, the obtained lithium mixture was subjectedto calcination for 5 hours at 900° C. in an air flow, cooled, and thensubjected to grinding, thereby providing a positive electrode activematerial. The obtained positive electrode active material wasLi_(1.02)Ni_(0.50)Co_(0.20)Mn_(0.30)O₂ in composition, and the analysiswith an X-ray diffractometer (from PANalytical, X'Pert PRO) confirmed asingle phase of a hexagonal lithium composite oxide. In addition, theorientation index at the (003) plane was 0.97, which was obtained fromthe X-ray diffraction waveform, and the site occupancy obtained fromRietveld analysis was 4.0% at 3 a sites with metal ions other thanlithium, whereas the site occupancy obtained therefrom was 5.0% at 3 bsites with lithium ions. The specific surface area measured by a BET(Brunauer, Emmett, Teller) method was 1.3 m²/g. Furthermore, a 2032-typecoin battery (coin-type battery 1) was prepared, and evaluated forinitial discharge capacity, cycle capacity maintenance rate, and ratecharacteristics.

Further, according to Example 1, Table 1 shows the evaluation results,besides the volume average particle size (Mv), aspect ratio, compositionratio evaluated in the same way as the nickel composite hydroxide. The[(D90−D10)/Mv] was equivalent to that of the nickel composite hydroxide.

Example 2

According to Example 2, a nickel composite hydroxide was obtained in thesame way as in Example 1, except that the pH in the nucleation step wasadjusted to 13.7 on the basis of a liquid temperature of 25° C. Thesecondary particles of the nickel composite hydroxide obtained were 9.6μm in volume average particle size (Mv), and 10.7 in aspect ratio.

According to Example 2, a positive electrode active material wasobtained and evaluated in the same way as in Example 1, except for theuse of the nickel composite hydroxide obtained. The evaluation resultsare shown in Tables 1 and 2.

Example 3

According to Example 3, a nickel composite hydroxide was obtained in thesame way as in Example 1, except that the pH in the nucleation step wasadjusted to 12.7 on the basis of a liquid temperature of 25° C. Thesecondary particles of the nickel composite hydroxide obtained were 11.8μm in volume average particle size (Mv), and 5.5 in aspect ratio.

According to Example 3, a positive electrode active material wasobtained and evaluated in the same way as in Example 1, except for theuse of the nickel composite hydroxide obtained. The evaluation resultsare shown in Tables 1 and 2.

Example 4

According to Example 4, a nickel composite hydroxide was obtained in thesame way as in Example 1, except that the pH in the particle growth stepwas adjusted to 12.3 on the basis of a liquid temperature of 25° C. Thesecondary particles of the nickel composite hydroxide obtained were 9.9μm in volume average particle size (Mv), and 4.6 in aspect ratio.

According to Example 4, a positive electrode active material wasobtained and evaluated in the same way as in Example 1, except for theuse of the nickel composite hydroxide obtained. The evaluation resultsare shown in Tables 1 and 2.

Example 5

According to Example 5, a nickel composite hydroxide was obtained in thesame way as in Example 1, except that the pH in the particle growth stepwas adjusted to 10.7 on the basis of a liquid temperature of 25° C. Thesecondary particles of the nickel composite hydroxide obtained were 11.4μm in volume average particle size (Mv), and 4.9 in aspect ratio.

According to Example 5, a positive electrode active material wasobtained and evaluated in the same way as in Example 1, except for theuse of the nickel composite hydroxide obtained. The evaluation resultsare shown in Tables 1 and 2.

Example 6

According to Example 6, a nickel composite hydroxide was obtained in thesame way as in Example 1, except that the oxygen concentration in thespace in the reaction tank was adjusted to 3.0 volume %. The secondaryparticles of the nickel composite hydroxide obtained were 10.1 μm involume average particle size (Mv), and 4.2 in aspect ratio.

According to Example 6, a positive electrode active material wasobtained and evaluated in the same way as in Example 1, except for theuse of the nickel composite hydroxide obtained. The evaluation resultsare shown in Tables 1 and 2.

Comparative Example 1

[Nucleation Step]

According to Comparative Example 1, 900 ml of pure water and 40 ml of 25mass % ammonia water were put in a crystallization reaction container of5 L in volume equipped with four baffle plates, and warmed to 60° C. ina thermostatic tank and a warming jacket while stirring at a revolvingspeed of 1000 rpm with six inclined blade paddles, and an aqueoussolution of 25 mass % sodium hydroxide was then added to adjust the pHof the solution in the reaction container to 12.6 on the basis of aliquid temperature of 25° C., thereby providing an unreacted aqueoussolution.

On the other hand, according to Comparative Example 1, an aqueoussolution including a nickel sulfate (Ni molar concentration: 1.00mol/L), a cobalt sulfate (Co molar concentration: 0.40 mol/L), and amanganese sulfate (Mn molar concentration: 0.60 mol/L) was prepared as araw material aqueous solution for nucleation.

According to Comparative Example 1, while stirring the unreacted aqueoussolution kept at 60° C., a specified amount of the raw material aqueoussolution for nucleation was supplied at 12.9 ml/min to the unreactedaqueous solution, and in addition, 25% ammonia water as a complexingagent at 1.5 ml/min, and an aqueous solution of 25 mass % sodiumhydroxide as a neutralizer were supplied thereto, thereby controllingthe solution such that the ammonia concentration was 10 g/L withconstant pH of 12.6 on the basis of a liquid temperature 25° C., andthus providing crystal nucleus-containing slurry.

[Particle Growth Step]

According to Comparative Example 1, an aqueous solution of 64 mass %sulfuric acid was added to the crystal nucleus-containing slurry toadjust the pH to 11.6 on the basis of a liquid temperature 25° C.,thereby providing slurry for particle growth. The mixed aqueous solutionprepared in the same way as the raw material aqueous solution fornucleation was supplied at 12.9 ml/min to the slurry for particlegrowth, and in addition, an aqueous solution of 25 mass % sodiumhydroxide was supplied thereto while supplying 25 mass % ammonia wateras a complexing agent, thereby controlling the slurry such that theammonia concentration was 10 g/L with constant pH of 11.6, and thusproducing a nickel composite hydroxide. Thereafter, the hydroxide waswashed with water, filtrated, and dried for 24 hours at 120° C. in theair atmosphere. The obtained nickel composite hydroxide was evaluated inthe same way. The nickel composite hydroxide wasNi_(0.50)Co_(0.20)Mn_(0.30)(OH)₂ in composition. In addition, the volumeaverage particle size (Mv) was 9.2 μm, and the [(D90−D10)/Mv] indicatinga particle size variation index was 0.48.

FIG. 6 shows a SEM observation result in Comparative Example 1. Theaspect ratio measured from the SEM observation was 1.1, and it has beenthus confirmed that the nickel composite hydroxide has substantiallyspherical hydroxide particles.

[Production and Evaluation of Positive Electrode Active Material]

According to Comparative Example 1, a positive electrode active materialwas obtained and evaluated in the same way as in Example 1, except forthe use of the nickel composite hydroxide obtained. The evaluationresults are shown in Tables 1 and 2. The obtained positive electrodeactive material was Li_(1.02)Ni_(0.50)Co_(0.20)Mn_(0.30)O₂ incomposition, and the analysis with an X-ray diffractometer (fromPANalytical, X'Pert PRO) confirmed a single phase of a hexagonal lithiumcomposite oxide.

-   Comparative Example 2

According to Comparative Example 2, a nickel composite hydroxide wasobtained in the same way as in Example 1, except that the pH in thenucleation step was adjusted to 12.0 on the basis of a liquidtemperature of 25° C. The secondary particles of the nickel compositehydroxide obtained were 11.8 μm in volume average particle size (Mv),and 2.5 in aspect ratio, and the average value was 1.6 μm for themaximum diameters projected from directions perpendicular to platesurfaces of plate-shaped primary particles.

According to Comparative Example 2, a positive electrode active materialwas obtained and evaluated in the same way as in Example 1, except forthe use of the nickel composite hydroxide obtained. The evaluationresults are shown in Tables 1 and 2.

Comparative Example 3

According to Comparative Example 3, a nickel composite hydroxide wasobtained in the same way as in Example 1, except that the pH in theparticle growth step was adjusted to 12.7 on the basis of a liquidtemperature of 25° C. The secondary particles of the nickel compositehydroxide obtained were 7.2 μm in volume average particle size (Mv), and2.0 in aspect ratio.

According to Comparative Example 3, a positive electrode active materialwas obtained and evaluated in the same way as in Example 1, except forthe use of the nickel composite hydroxide obtained. The evaluationresults are shown in Tables 1 and 2.

Comparative Example 4

According to Comparative Example 4, a nickel composite hydroxide wasobtained in the same way as in Example 1, except that the space in thereaction tank was changed to the air atmosphere. The secondary particlesof the nickel composite hydroxide obtained were 4.1 μm in volume averageparticle size (Mv), and 1.3 in aspect ratio.

According to Comparative Example 4, a positive electrode active materialwas obtained and evaluated in the same way as in Example 1, except forthe use of the nickel composite hydroxide obtained. The evaluationresults are shown in Tables 1 and 2.

TABLE 1 Volume average Orientation particle Aspect index at a size (μm)ratio (003) plane Example 1 10.6 6.3 0.97 Example 2 9.6 10.7 0.94Example 3 11.8 5.5 0.99 Example 4 9.9 4.6 0.95 Example 5 11.4 4.9 0.98Example 6 10.1 4.2 0.99 Comparative 9.2 1.1 1.04 Example 1 Comparative11.8 2.5 1.01 Example 2 Comparative 7.2 2.0 1.03 Example 3 Comparative4.1 1.3 1.15 Example 4

TABLE 2 Discharge Capacity capacity maintenance Initial for 5 C/ ratedischarge discharge after 200 capacity capacity for cycle (mAh/g) 0.2 C(%) (%) Example 1 168 68.5 92 Example 2 164 68.9 90 Example 3 168 67.692 Example 4 165 64.2 90 Example 5 168 65.1 91 Example 6 165 64.2 91Comparative 167 60.2 90 Example 1 Comparative 165 60.8 89 Example 2Comparative 166 61.7 90 Example 3 Comparative 163 56.8 90 Example 4

According to Examples 1 to 6, the nickel composite hydroxides wereobtained which were 3 to 20 in aspect ratio and 4 μm to 20 μm in volumeaverage particle size (Mv), and the plate-shaped lithium compositeoxides obtained with the use of the nickel composite hydroxides asprecursors were also equivalent to the nickel composite hydroxides inthe values of the aspect ratio and volume average particle size. It hasbeen confirmed that the coin batteries using the lithium compositeoxides as positive electrode active materials are superior in batterycharacteristics (initial discharge capacity, cycle capacity maintenancerate, rate characteristics).

On the other hand, the lithium composite oxides which failed to meet theaspect ratio of 3 to 20 were obtained according to Comparative Examples1 to 4. In addition, it has been determined that the coin batteriesusing the composite oxides as positive electrode active materials areinferior in battery characteristics.

GLOSSARY OF DRAWING REFERENCES

-   1 . . . coin-type battery, 2 . . . case, 2 a . . . positive    electrode can, 2 b . . . negative electrode can, 2 c . . . gasket, 3    . . . electrode, 3 a . . . positive electrode, 3 b . . . negative    electrode, 3 c . . . separator

1. A nickel composite hydroxide represented byNi_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (x, y, z, and A in the formulafall within ranges of: 0<x≦0.35; 0≦y≦0.35; 0≦z≦0.1; and 0≦A≦0.5, x, y,and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W), thenickel composite hydroxide comprising plate-shaped secondary particlesaggregated with overlaps between plate surfaces of multiple plate-shapedprimary particles, wherein shapes projected from directionsperpendicular to the plate surfaces of the plate-shaped primaryparticles are any plane projection shape of spherical, elliptical,oblong, and massive shapes, and the secondary particles have an aspectratio of 3 to 20, and a volume average particle size (Mv) of 4 μm to 20μm measured by a laser diffraction scattering method.
 2. The nickelcomposite hydroxide according to claim 1, wherein [(D90−D10)/Mv]indicating a particle size variation index is 0.70 or less, thevariation index calculated from D90 and D10 in a particle sizedistribution obtained by a laser diffraction scattering method and thevolume average particle size (Mv).
 3. The nickel composite hydroxideaccording to claim 1, wherein an average value is 1 μm to 5 μm formaximum diameters of the plate-shaped primary particles projected fromdirections perpendicular to plate surfaces of the secondary particles.4. The nickel composite hydroxide according to claim 1, wherein theplate-shaped primary particles comprise therein at least a concentrationlayer of cobalt.
 5. The nickel composite hydroxide according to claim 4,wherein the concentration layer is 0.01 μm to 1 μm in thickness.
 6. Aproduction process for producing a nickel composite hydroxiderepresented by Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)_(2+A) (x, y, z, and Ain the formula fall within ranges of: 0<x≦0.35; 0≦y≦0.35; 0≦z≦0.1; and0≦A≦0.5, x, y, and z meet 0<x+y+z≦0.7, and M in the formula representsat least one additive element selected from V, Mg, Al, Ti, Mo, Nb, Zr,and W), the process comprising: a nucleation step of generatingplate-shaped crystal nuclei by adjusting an aqueous solution fornucleation, comprising a metal compound containing cobalt, wherein acontent of cobalt is 90 atom % or more with respect to all metalelements, to an pH value of 12.5 or more on the basis of a liquidtemperature of 25° C. in a non-oxidizing atmosphere with an oxygenconcentration of 5 volume % or less; and a particle growth step ofcausing growth of the plate-shaped crystal nuclei until an aspect ratiofalls within a range of 3 to 20, by adjusting slurry for particlegrowth, containing the plate-shaped crystal nuclei formed in thenucleation step, in a non-oxidizing atmosphere with an oxygenconcentration of 5 volume % or less, such that a pH value of the slurryis 10.5 to 12.5 on the basis of a liquid temperature of 25° C., andlower than the pH value in the nucleation step, and supplying a mixedaqueous solution comprising a metal compound containing at least nickelto the slurry for particle growth.
 7. The process for producing a nickelcomposite hydroxide according to claim 6, wherein nucleation isdeveloped in a non-oxidizing atmosphere with an oxygen concentration of2 volume % or less in the nucleation step.
 8. The process for producinga nickel composite hydroxide according to claim 6, wherein the slurryfor particle growth has an ammonia concentration adjusted to 5 g/L to 20g/L in the particle growth step.
 9. The process for producing a nickelcomposite hydroxide according to claim 6, wherein plate-shaped crystalnucleus-containing slurry with a pH value adjusted is used as the slurryfor particle growth, the plate-shaped crystal nucleus-containing slurrycontaining the plate-shaped crystal nuclei obtained in the nucleationstep.
 10. A positive electrode active material for a non-aqueouselectrolyte secondary battery, the positive electrode active materialcomprising a lithium-nickel composite oxide represented byLi_(1+u)Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)O₂ (u, x, y, and z in the formulafall within ranges of: −0.05≦u≦0.50; 0<x≦0.35; 0≦y≦0.35; and 0≦z≦0.1, x,y, and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W), thelithium-nickel composite oxide having a hexagonal layered structure,wherein lithium-nickel composite oxide comprises plate-shaped secondaryparticles aggregated with overlaps between plate surfaces of multipleplate-shaped primary particles, shapes projected from directionsperpendicular to the plate surfaces of the plate-shaped primaryparticles are any plane projection shape of spherical, elliptical,oblong, and massive shapes, and the secondary particles have an aspectratio of 3 to 20, and a volume average particle size (Mv) of 4 μm to 20μm measured by a laser diffraction scattering method.
 11. The positiveelectrode active material for a non-aqueous electrolyte secondarybattery according to claim 10, wherein the positive electrode activematerial has a specific surface area of 0.3 m²/g to 2 m²/g.
 12. Thepositive electrode active material for a non-aqueous electrolytesecondary battery according to claim 10, wherein [(D90−D10)/Mv]indicating a particle size variation index is 0.75 or less, thevariation index calculated from D90 and D10 in a particle sizedistribution obtained by a laser diffraction scattering method and thevolume average particle size (Mv).
 13. The positive electrode activematerial for a non-aqueous electrolyte secondary battery according toclaim 10, wherein a site occupancy is 7% or less at 3 a sites with metalions other than lithium, and a site occupancy is 7% or less at 3 b siteswith lithium ions, the site occupancies obtained from Rietveld analysiswith X-ray diffraction analysis.
 14. The positive electrode activematerial for a non-aqueous electrolyte secondary battery according toclaim 10, wherein an orientation index at a (003) plane is 0.9 to 1.1,the orientation index found by X-ray diffraction analysis.
 15. A processfor producing a positive electrode active material for a non-aqueouselectrolyte secondary battery, the positive electrode active materialcomprising a lithium-nickel composite oxide represented byLi_(1+u)Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)O₂ (u, x, y, and z in the formulafall within ranges of: −0.05≦u≦0.50; 0<x≦0.35; 0≦y≦0.35; and 0≦z≦0.1, x,y, and z meet 0<x+y+z≦0.7, and M in the formula represents at least oneadditive element selected from V, Mg, Al, Ti, Mo, Nb, Zr, and W), thelithium-nickel composite oxide having a hexagonal layered structure, theprocess comprising: a mixing step of forming a lithium mixture by mixingthe nickel composite hydroxide according to claim 1 with a lithiumcompound; and a calcining step of calcining the lithium mixture formedin the mixing step at a temperature of 650° C. to 980° C. in anoxidizing atmosphere.
 16. The process for producing a positive electrodeactive material for a non-aqueous electrolyte secondary batteryaccording to claim 15, wherein a ratio (Li/Me) of the lithium atomnumber (Li) to a sum (Me) of the atom numbers of metals other thanlithium included in the lithium mixture is 0.95 to 1.5.
 17. The processfor producing a positive electrode active material for a non-aqueouselectrolyte secondary battery according to claim 15, the process furthercomprising, before the mixing step, a heat treatment step of applying aheat treatment to the nickel composite hydroxide at a temperature of300° C. to 750° C. in a non-reducing atmosphere.
 18. The process forproducing a positive electrode active material for a non-aqueouselectrolyte secondary battery according to claim 15, wherein theoxidizing atmosphere in the calcining step is an atmosphere containing18 volume % to 100 volume % of oxygen.
 19. A non-aqueous electrolytesecondary battery comprising a positive electrode, a negative electrode,a non-aqueous electrolyte, and a separator, wherein the positiveelectrode is formed from the positive electrode active material for anon-aqueous electrolyte secondary battery according to claim 10.